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[^ Apple II

Reference Manual

For He Only

I J

Notice

Apple Computer, Inc. reserves the right to make improvements in the
product described in this manual at any time and without notice.

Disclaimer of All Warranties and Liabilities

Apple Computer, Inc. makes no warranties, either express or implied, with
respect to this manual or with respect to the software described in this
manual, its quality, performance, merchantability, or fitness for any
particular purpose. Apple Computer, Inc. software is sold or licensed "as
is." The entire risk as to its quality and performance is with the buyer.
Should the programs prove defective following their purchase, the buyer
(and not Apple Computer, Inc., its distributor, or its retailer) assumes the
entire cost of all necessary servicing, repair, or correction and any
incidental or consequential damages. In no event will Apple Computer, Inc.
be liable for direct, indirect, incidental, or consequential damages resulting
from any defect in the software, even if Apple Computer, Inc. has been
advised of the possiblity of such damages. Some states do not allow the
exclusion or limitation of implied warranties or liability for incidental or
consequential damages, so the above limitation or exclusion may not apply
to you.

This manual is copyrighted. All rights are reserved. This document may
not, in whole or part, be copied, photocopied, reproduced, translated or
reduced to any electronic medium or machine readable form without prior
consent, in writing, from Apple Computer, Inc.

The word Apple and the Apple logo are registered trademarks of
Apple Computer, Inc.

Simultaneously published in the U.S. A and Canada.

Warning

This equipment has been certified to comply with the limits for a
Class B computing device, pursuant to Subpart J of Part 15 of FCC
Rules. Only peripherals (computer input/output devices, terminals,
printers, etc.) certified to comply with the Class B limits may be
attached to this computer. Operation with non-certified peripherals is
likely to result in interference to radio and TV reception.

Written by Allen Watson of the Apple PCSD
Publications Department

Reorder Apple Product A2L2005

Apple II

Reference Manual

'.'■■ ; - ; •
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Radio and Television Interference

The equipment described in this manual generates and uses radio-
frequency energy. If it is not installed and used properly, that is, in
strict accordance with our instructions, it may cause interference
with radio and television reception.

This equipment has been tested and complies with the limits for a
Class B computing device in accordance with the specifications in
Subpart J, Part 15, of FCC rules. These rules are designed to
provide reasonable protection against such interference in a
residential installation. However, there is no guarantee that the
interference will not occur in a particular installation, especially if
you use a "rabbit ear" television antenna. (A "rabbit ear" antenna is
the telescoping-rod type usually contained on TV receivers.)

You can determine whether your computer is causing interference
by turning it off. If the interference stops, it was probably caused
by the computer or its peripheral devices. To further isolate the
problem:

• Disconnect the peripheral devices and their input/output cables
one at a time. If the interference stops, it is caused by either
the peripheral device or its I/O cable. These devices usually
require shielded I/O cables. For Apple peripheral devices, you
can obtain the proper shielded cable from your dealer. For non-
Apple peripheral devices, contact the manufacturer or dealer
for assistance.

If your computer does cause interference to radio or television
reception, you can try to correct the interference by using one or
more of the following measures:

• Turn the TV or radio antenna until the interference stops.

• Move the computer to one side or the other of the TV or radio.

• Move the computer farther away from the TV or radio.

• Plug the computer into an outlet that is on a different circuit
than the TV or radio. (That is, make certain the computer and
the radio or television set are on circuits controlled by different
circuit breakers or fuses.)

• Consider installing a rooftop television antenna with coaxial
cable lead-in between the antenna and TV.

If necessary, you should consult your dealer or an experienced
radio/television technician for additional suggestions. You may find
helpful the following booklet, prepared by the Federal
Communications Commission:

"How to Identify and Resolve Radio-TV Interference Problems"

This booklet is available from the U.S. Government Printing Office,
Washington, DC 20402, stock number 004-000-00345-4.

-.,.

ContenH

Table of Contents

Foreword

xiii Contents of This Manual

xv Symbols Used in This Manual

Introduction

1 Removing the Cover

5 The Keyboard

5 The Speaker

5 The Power Supply

6 The Circuit Board

7 Connectors on the Circuit Board

8 Connectors on the Back Panel

i: 2

Built-in I/O Devices

1 1 The Keyboard

13 Reading the Keyboard

17 The Video-display Generator

19 Text Modes

19 Text Character Sets

21 40-column versus 80-column Text

22 Graphics Modes

22 Low-resolution Graphics

23 High-resolution Graphics

26 Display Pages

27 Display Mode Switching

29 Addressing Display Pages Directly

35 Secondary Inputs and Outputs

35 The Speaker

36 Cassette Input and Output

37 The Hand Control Connector Signals

Annunciator Outputs

Strobe Output

Switch Inputs

Analog Inputs

Summary of Secondary I/O Locations

Built-in I/O Firmware

Using the I/O Subroutines

Apple II Compatibility

The 80-column Firmware

The Old Monitor

The Standard I/O Links

Standard Output Features

COUT Output Subroutine

Control Characters with C0UT1

The Stop-List Feature

The Text Window

Inverse and Flashing Text

Standard Input Features

RDKEY Input Subroutine

KEY IN Input Subroutine

Escape Codes with key in

Cursor Motion in Escape Mode

GETLN Input Subroutine

Editing with GETLN

Cancel Line

Backspace

Retype

■.-— i

Memory Organization 59

61 Main Memory Map

63 RAM Memory Allocation

63 Reserved Memory Pages

64 Page Zero
64 The 6502 Stack

64 The Input Buffer

65 Link-address Storage
65 The Display Buffers

68 Bank-switched Memory

69 Setting Bank Switches *— '
71 Auxiliary Memory and Firmware
73 Memory Mode Switching
76 Auxiliary-memory Subroutines

-A

77 Moving Data to Auxiliary Memory

78 Transferring Control to Auxiliary Memory

79 The Reset Routine

80 The Cold-start Procedure

80 The Warm-start Procedure
— i* 81 Forced Cold Start

81 The Reset Vector
83 Automatic Self-test

Using the Monitor 85

C 87 Invoking the Monitor

88 Syntax of Monitor Commands
^^_ 89 Monitor Memory Commands

89 Examining Memory Contents
89 Memory Dump

^ 92 Changing Memory Contents

92 Changing One Byte

93 Changing Consecutive Locations

94 Moving Data in Memory

96 Comparing Data in Memory

97 Monitor Register Command

97 Examining and Changing Registers

98 Monitor Cassette Tape Commands

98 Saving Data on Tape

99 Reading Data from Tape

mmM 101 Miscellaneous Monitor Commands

101 Display Inverse and Normal

_ 102 Back to BASIC

_Jf 102 Redirecting Input and Output

103 Hexadecimal Arithmetic

104 Special Tricks with the Monitor
m jM 104 Multiple Command Lines

104 Filling Memory

106 Repeating Commands

106 Creating Your Own Commands

107 Machine-language Programs

107 Running a Program

108 Disassembled Programs
110 The Mini-Assembler

113 Mini-Assembler Instruction Formats

115 Summary of Monitor Commands

VII

Programming for Accessory Cards 119

121 Peripheral-card Memory Spaces

122 Peripheral-card I/O Space

122 Peripheral-card ROM Space

123 Expansion ROM Space

125 Peripheral-card RAM Space

126 I/O Programming Suggestions

127 Finding the Slot Number

127 I/O Addressing

128 RAM Addressing

129 Changing the Standard I/O Links
131 Using Interrupts

131 Other Uses of I/O Memory Space

132 Switching I/O Memory

Hardware Implementation 134

137 Environmental Specifications

138 The Power Supply

139 The Power Connector

140 The 6502 Microprocessor

141 6502 Timing

143 The Custom Integrated Circuits

143 The Memory Management Unit

145 The Input/Output Unit

147 The PAL Circuit

148 Memory Addressing

148 ROM Addressing

149 RAM Addressing

149 Dynamic-RAM Refreshment

151 Dynamic-RAM Timing

152 The Video Display

1 53 The Video Counters

154 Display Memory Addressing
154 Display Address Mapping
158 Video Display Modes

158 Text Displays

160 Low-resolution Display

161 High-resolution Display

163 Video Output Signals

164 Built-in I/O Circuits

164 The Keyboard

165 Connecting a Keypad

166 Cassette I/O

166 The Speaker

167 Game I/O Signals

^ A

* B

169 Expanding the Apple lie

169 The Expansion Slots

169 The Peripheral Address Bus

170 The Peripheral Data Bus
170 Loading and Driving Rules

170 Interrupt and DMA Daisy Chains

174 Video Signals on Slot 7

174 The Auxiliary Slot

175 80-column Display Signals

The 6502 Instruction Set 185

Tables 197

Directory of Built-in Subroutines 217

Differences Between the Apple He

and Apple II Plus 225

Glossary 231

Bibliography 253

Index 257

266 Numbers

266 Cast of Characters

List of Figures

Figure

1-1.

Figure

1-2.

Figure

1-3.

Figure

1-4.

Figure

1-5.

Figure

1-6.

Figure

1-7.

Figure

1-8.

Figure

2-1.

Figure

2-2.

Figure

2-3.

Figure

2-4.

Figure

2-5.

Figure

2-6.

Figure

2-7.

Figure

2-8.

Figure

4-1.

Figure

4-2.

Figure

4-3.

Figure

4-4.

124

Figure

6-1.

125

Figure 6-2.

132

Figure

6-3.

142

Figure

7-1.

143

Figure

7-2.

145

Figure

7-3.

147

Figure

7-4.

149

Figure

7-5.

149

Figure

7-6.

149

Figure

7-7.

150

Figure

7-8.

152

Figure

7-9.

155

Figure

7-10.

156

Figure

7-11.

159

Figure

7-12.

171

Figure

7-13.

179

Figure

7- 14a

180

Figure

7-1 4b

Exploded Diagram of the Apple Me

Removing the Cover

The Apple lie With the Cover Off _

Apple lie Keyboard *

Circuit Board

Expansion Slots ~-

Auxiliary Slot *

Back Panel Connectors

The Keyboard

40-column Text Display

80-column Text Display

High-resolution Display Bits Jj

Map of 40-column Text Display

Map of 80-column Text Display

Map of Low-resolution Graphics

Display

Map of High-resolution Graphics

Display y

System Memory Map

RAM Allocation Map «-

Bank-switched Memory Map

Memory Map with Auxiliary Memory

Expansion ROM Enable Circuit
ROM Disable Address Decoding
I/O Memory Map

■
6502 Timing Signals
The MMU Pinouts

The IOU Pinouts |

The PAL Pinouts
The 2364 ROM Pinouts
The 2316 ROM Pinouts |

The 2333 ROM Pinouts
The 64K RAM Pinouts

RAM Timing Signals |

Display Address Transformation
40-column Text Display Memory
Video Timing Signals ■

Peripheral-signal Timing
Schematic Diagram, part 1
Schematic Diagram, part 2 2

181 Figure 7-1 4c. Schematic Diagram, part 3

182 Figure 7-14d. Schematic Diagram, part 4

List of Tables

12 Table 2-1.

13.

197 Table 2-2.

14,

198 Table 2-3a.

15,

199 Table 2-3b.

16,

200 Table 2-4.

18 Table 2-5.

20,

201 Table 2-6.

23,

201 Table 2-7.

25,

201 Table 2-8.

27,

202 Table 2-9.

28,

203 Table 2-10.

38,

204 Table 2-1 1 .

40,

205 Table 2-12.

43 Table 3-1 .

44 Table 3-2.

48,

206 Table 3-3a.

49,

207 Table 3-3b.

52,

207 Table 3-4.

53 Table 3-5.

55,

208 Table 3-6.

57 Table 3-7.

66 Table 4-1.

66 Table 4-2.

67 Table 4-3.

67 Table 4-4.

69,

209 Table 4-5.

75,

210 Table 4-6.

76 Table 4-7.

77 Table 4-8.

78 Table 4-9.

82,

211 Table 4-10.

114 Table 5-1.

122,

212 Table 6-1.

123,

212 Table 6-2.

125,

213 Table 6-3.

128,

214 Table 6-4.

133,

214 Table 6-5.

Apple Me Keyboard Specifications
Keyboard Memory Locations
Keys and ASCII Codes
Keys and ASCII Codes
The ASCII Character Set
Video Display Specifications
The Display Character Sets
Low-resolution Graphics Colors
High-resolution Graphics Colors
Video Display Page Locations
Display Soft Switches
Annunciator Memory Locations
Secondary I/O Memory Locations

Standard I/O Subroutines

Apple II Mode

Control Characters with cduti

Control Characters with cduti ,

continued

Text Window Memory Locations

Text Format Control Values

Escape Codes

Prompt Characters

Monitor Zero-page Usage
Applesoft Zero-page Usage
Integer BASIC Zero-page Usage
DOS 3.3 Zero-page Usage
Bank Select Switches
Auxiliary-memory Select Switches
Auxiliary-memory Routines
Parameters for auxmqve Routine
Parameters for xfer Routine
Page 3 Vectors

Mini-assembler Address Formats

Peripheral-card I/O Memory Locations
Peripheral-card ROM Memory Locations
Peripheral-card RAM Memory Locations
Peripheral-card I/O Base Addresses
I/O Memory Switches

137 Table 7-1.

138 Table 7-2.

139 Table 7-3.

140 Table 7-4.

141 Table 7-5.
144 Table 7-6.

146 Table 7-7.

147 Table 7-8.

150 Table 7-9.

151 Table 7-10.

157 Table 7-11.

158 Table 7-12.

160 Table
163 Table
165 Table

165 Table

166 Table
168 Table

172 Table

173 Table

174 Table

176 Table

177 Table

178 Table

7-13.

7-14.

7-15.

7-16.

7-17.

7-18.

7-1 9a.

7-1 9b.

7-1 9c.

7-20a.

7-20b.

7-20c.

Summary of Environmental

Specifications

Power Supply Specifications

Power Connector Signal Specifications

6502 Microprocessor Specifications

6502 Timing Signal Descriptions

The MMU Signal Descriptions

The IOU Signal Descriptions

The PAL Signal Descriptions

RAM Address Multiplexing

Dynamic RAM Timing Signals

Display Memory Addressing

Memory Address Bits for Display

Modes

Character-Generator Control Signals

Internal Video Connector Signals

Keyboard Connector Signals

Keypad Connector Signals

Speaker Connector Signals

Game I/O Connector Signals

Expansion Slot Signals

Expansion Slot Signals, continued

Auxiliary Slot Signals

Auxiliary Slot Signals, continued

XII

Foreword

This is the reference manual for the Apple lie personal computer.
It contains detailed descriptions of all of the hardware and
firmware that make up the Apple lie and provides the technical
information that peripheral-card designers and programmers
need. There is an Addendum, bound separately, that contains
source listings of the built-in firmware.

This manual contains a lot of information about the way the
Apple lie works, but it doesn't tell you how to use the Apple Me.
For this, you should read the other Apple lie manuals, especially
the following:

• The Apple lie Owner's Manual

• The Applesoft Tutorial

This manual is designed to answer the question, What's inside
the box? It describes the internal operation of the Apple Me as
completely as possible in a single volume. The criterion for
deciding to include an item of information was whether it would
help an assembly-language programmer or peripheral designer.

Contents of This Manual

The material in this manual is presented roughly in order of
increasing intimacy with the hardware; the farther you go in the
manual, the more technical the material becomes. The main
subject areas are

• Introduction: Foreword and Chapter 1

• Use of built-in features: Chapters 2 and 3

• How the memory is organized: Chapter 4

• Information for programmers: Chapters 5 and 6

XIII

• Hardware implementation: Chapter 7

• Additional information: Appendices and Addendum

Chapter 1 identifies the main parts of the Apple lie and tells
where in the manual each part is described.

The next two chapters describe the built-in input and output
features of the Apple Me. This part of the manual includes
information you need for low-level programming on the Apple He.
Chapter 2 describes the built-in I/O features and Chapter 3 tells
you how to use the firmware that supports them.

Chapter 4 describes the way the Apple lie's memory space is
organized, including the allocation of programmable memory for
the video display buffers.

Chapter 5 is a user manual for the Monitor that is included in the
built-in firmware. The Monitor is a system program that you can
use for program debugging at the machine level.

Chapter 6 describes the programmable features of the peripheral-
card connectors and gives guidelines for their use.

Chapter 7 is a detailed description of the hardware that
implements the features described in the earlier chapters. This
information is included primarily for programmers and peripheral-
card designers, but it will also help you if you just want to
understand more about the way the Apple Me works.

Additional reference information appears in the appendices.
Appendix A is the manufacturer's description of the 6502
instruction set.

Appendix B contains additional copies of some of the tables that
appear in the body of the manual. The ones you will need to
refer to often are duplicated here for easy reference.

Appendix C is a directory of the built-in I/O subroutines, including
their functions and starting addresses.

Appendix D lists the differences between the Apple Me and the
earlier Apple II and Apple II Plus models and tells you which
sections to look at for more information.

xiv

Following Appendix D is a glossary defining many of the
technical terms used in this manual. Some terms that describe
the use of the Apple He are defined in the glossaries of the other
manuals listed above.

«••£ Following the appendices, there is a selected bibliography of

sources of additional information.

mjI The Addendum to this manual contains the source listing of the

Monitor firmware. You can refer to it to find out more about the
operation of the Monitor subroutines listed in Appendix C.

■s

Symbols Used in This Manual

Special text in this manual is set off in several different ways, as
shown in these examples.

Information that appears on the display screen is
set off by this screen-shaped outline.

Warning

Important warnings appear in boxes like this.

Captions, definitions, and other short Information that is useful but is incidental to the text appears in grey

items appear in marginal glosses like boxes like this. You may want to skip over such boxes and return to

tnis - them later.

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Introduction

4 Removing the Cover

5 The Keyboard
5 The Speaker

5 The Power Supply

6 The Circuit Board

7 Connectors on the Circuit Board

8 Connectors on the Back Panel

Introduction

Chapter 1

Introduction

This first chapter introduces you to the Apple He itself. It shows
you what the inside looks like, identifies the major components
that make up the machine, and tells you where to find
information about each one. These major components are shown
in the diagram in Figure 1.1.

Figure 1-1 Exploded Diagram of the
Apple lie

Introduction

Removing the Cover

Remove the cover of the Apple Me by pulling up on the back
edge until the fasteners on either side pop loose, then move the
cover an inch or so towards the rear of the machine to free the
front of the cover, as shown in Figure 1-2. What you will see is
shown in Figure 1-3.

*—

Figure 1-2 Removing the Cover

Figure 1-3 The Apple lie with the
Cover Off

Warning

There is a red LED (light-emitting diode) inside the Apple lie, in the
left rear corner of the circuit board. If the LED is on, it means that
the power is on and you must turn it off before you insert or
remove anything. To avoid damaging the Apple lie, don't even
THINK of changing anything inside it without first turning off the
power.

^ !

Introduction

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The Keyboard

The keyboard is the Apple lie's primary input device. As shown in
Figure 1-4, it has a normal typewriter layout, upper- and
lowercase, with all of the special characters in the ASCII
character set. (ASCII stands for American Standard Code for
Information Interchange.) The keyboard is fully integrated into the
machine; its operation is described in the first part of Chapter 2.
Firmware subroutines for reading the keyboard are described in
Chapter 3.

Figure 1-4 Apple lie Keyboard

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The Speaker

The Apple Me has a small loudspeaker in the bottom of the case,
as shown in Figure 1-1. The speaker enables Apple Me programs
to produce a variety of sounds that make the programs more
useful and interesting. The way programs control the speaker is
described in Chapter 2.

The Power Supply

The power supply is inside the flat metal box along the left side
of the interior of the Apple Me. It provides power for the main
board and for any peripheral cards installed in the Apple Me.

The power supply produces four different voltages: +5V, -5V,
+ 12V, and -12V. It is a high-efficiency switching supply, and
includes special circuits that protect it and the rest of the
Apple Me against short circuits and other mishaps. Complete
specifications of the Apple Me power supply appear in Chapter 7.

The Keyboard

Figure 1-5 Circuit Board

The power switch and the socket for the power cord are mounted
directly on the back of the power supply's metal case. This
mounting ensures that all the circuits that carry dangerous
voltages are inside the power supply. Do not defeat this design
feature by attempting to open the power supply.

The Circuit Board

All of the electronic parts of the Apple Me are attached to the
circuit board, which is mounted flat in the bottom of the case.

Figure 1-5 shows the main integrated circuits (ICs) in the
Apple Me. They are the central processing unit (CPU), the
keyboard encoder and read-only memory (ROM), the two
interpreter ROMs, and the custom integrated circuits: the Input
Output Unit (IOU) and the Memory Management Unit (MMU).

The CPU is a 6502B microprocessor. The 6502B is a high-speed
version of the 6502, which is an eight-bit microprocessor with a
sixteen-bit address bus. It uses instruction pipelining for faster
processing than comparable microprocessors. In the Apple Me,
the 6502B runs at 1 MHz and performs up to 500,000 eight-bit
operations per second. The specifications of the 6502B are given
in Chapter 7; the 6502 instruction set is given in Appendix A.

The keyboard is decoded by an AY-3600-type integrated circuit
and a read-only memory (ROM). These devices are described in
Chapter 7.

The interpreter ROMs are integrated circuits that contain the
Applesoft BASIC interpreter. The ROMs are described in
Chapter 7. The Applesoft language is described in the Applesoft
Tutorial and the Applesoft Reference Manual.

Two of the large ICs are custom-made for the Apple Me: the
MMU and the IOU. The MMU IC contains most of the logic that
controls memory addressing in the Apple Me. The organization of
the memory is described in Chapter 4; the circuitry in the MMU
itself is described in Chapter 7.

The IOU IC contains most of the logic that controls the built-in
input/output features of the Apple Me. These features are
described in Chapter 2 and Chapter 3; the IOU circuits are
described in Chapter 7.

Introduction

■HHHHnHi

Connectors on The Circuit Board

The seven slots lined up along the back of the Apple lie circuit
board are the expansion slots, sometimes called peripheral slots
(see Figure 1 -6). These slots make it possible to attach additional
hardware to the Apple lie. Chapter 6 tells you how your programs
deal with the devices that plug into these slots; Chapter 7
describes the circuitry for the slots themselves.

Figure 1-6 Expansion Slots

APPLE Ojr.pJTER INC.: r
830-0064-* Q 1S82|

—

The large slot next to the left-hand side of the circuit board is the
auxiliary slot (Figure 1-7). If your Apple lie has an Apple lie 80-
column text card, it will be installed in this slot. The 80-column
display option is fully integrated into the Apple lie; it is described
along with the other display features in Chapter 2. The hardware
and firmware interfaces to this card are described in Chapter 7.

Connectors on The Circuit Board

Figure 1-7 Auxiliary Slot

Figure 1-8 Back Panel Connectors

There are also smaller connectors for game I/O and for an
internal RF (radio frequency) modulator. These connectors are
described in Chapter 7.

Connectors on the Back Panel

The back of the Apple lie has two miniature phone jacks for
connecting a cassette recorder, an RCA-type jack for a video
monitor, and a 9-pin D-type miniature connector for the hand
controls, as shown in Figure 1-8. In addition to these, there are
spaces for additional connectors used with the peripheral cards
installed in the Apple He. The installation manuals for the
peripheral cards contain instructions for installing the
peripheral connectors.

Introduction

Chapter 2

Built-in I/O Devices

11 The Keyboard

13 Reading the Keyboard

17 The Video-display Generator

19 Text Modes

19 Text Character Sets

21 40-column versus 80-column Text

22 Graphics Modes

22 Low-resolution Graphics

23 High-resolution Graphics

26 Display Pages

27 Display Mode Switching

29 Addressing Display Pages Directly

35 Secondary Inputs and Outputs

35 The Speaker

36 Cassette Input and Output

37 The Hand Control Connector Signals

37 Annunciator Outputs

38 Strobe Output

38 Switch Inputs

39 Analog Inputs

40 Summary of Secondary I/O Locations

Built-in I/O Devices

—J

■ ■■ ■ ■ '

I— *

" I

Chapter 2

Built-in I/O Devices

This chapter describes the input and output (I/O) devices built
into the Apple lie in terms of their functions and the way they are
used by programs. The built-in I/O devices are

keyboard

video-display generator

speaker

cassette input and output

game input and output

At the lowest level, programs use the built-in I/O devices by
reading and writing to dedicated memory locations. This chapter
lists these locations for each I/O device. It also gives the
locations of the internal soft-switches that select the different
display modes of the Apple He. For descriptions of the built-in
I/O hardware, refer to Chapter 7.

This method of input and output — loading and storing directly to
specific locations in memory — is not the only method you can use.
For many of your programs, it may be more convenient to call the
built-in I/O routines stored in the Apple lie's firmware. These
firmware routines are described in Chapter 3.

The Keyboard

The primary input device of the Apple Me is its built-in keyboard.
The keyboard has 63 keys and is similar to the keyboard of a
typewriter. The Apple lie keyboard has automatic repeat on all
keys: hold the key down to repeat. It also has N-key rollover,
which means that you can hold down any number of keys while
typing another. Of course, if you hold the keys down much longer

The Keyboard

Figure 2-1 The Keyboard

than the length of time you would hold them down during normal
typing, the automatic-repeat function will start repeating the last
key you pressed.

The keyboard arrangement shown in Figure 2-1 is the standard
one used in the United States. The specifications for the
keyboard are given in Table 2-1. Apple lie's manufactured for
sale in Europe have a slightly different standard keyboard
arrangement and include provisions for switching between two
different arrangements.

ESC

1
1

#
3

s %

4 5

A I & * (

6 1 7 8 9

" ) - +

o - =

DELETE

RFSLT

TAB

W E

Y U 1

{ ) I
P C 3 \

CONTROL

A S

D F G

H J K

L i

RETURN

SHIFT 2 V

< > ?

B N M . /

SHIFT

CAPS
LOCK

• - -

I t

In addition to the keys normally used for typing characters, there
are four cursor-control keys with arrows: left, right, down, and up.
The cursor-control keys can be read the same as other keys;
their codes are $08, $15, $0A, and $0B (see Table 2-3a).

Table 2-1 Apple lie Keyboard
Specifications

Number of keys: 63

Character encoding: ASCII

Number of codes: 128
Special keys:

Rollover:

CONTROL , SHIFT , CAPS LOCK , IESC_

RESET I, LEFT-ARROW , RIGHT-ARROW

UP-ARROW , I DOWN-ARROW |, I OPEN-APPLE |

SOLID-APPLE

N-key

Electrical interface: AY-5-3600 keyboard encoder

Built-in I/O Devices

5
LZ

Four special keys, | control [ , | shift! , 1 CAPS LOCK - ], and fESc]
change the codes generated by the other keys. The [ CONTROL]
key is similar to the ASCII CTRL key. Three other keys have
special functions: the | RESET 1 key, and two keys marked with
appl es, one outlined, or o pen, and on e solid, or closed. Pressing
the 1 RESET 1 key with the | control | key depressed resets the
Apple He, as described in Chapter 4. The Apple keys are
connected to the one-bit game inputs, described later in this
chapter.

The electrical interface between the Apple lie and the keyboard is
a ribbon cable with a 26-pin connector. This cable carries the
keyboard signals to the encoding circuitry on the main board. A
complete description of the electrical interface to the keyboard is
given in Chapter 7.

Table 2-2 Keyboard Memory
Locations

Reading the Keyboard

The keyboard encoder and ROM generate all 128 ASCII codes,
so all of the special character codes in the ASCII character set
are available from the keyboard. Machine-language programs
obtain character codes from the keyboard by reading a byte from
the keyboard-data location shown in Table 2-2.

Location
Hex

Decimal

Description

$C000 49152 -16384 Keyboard data and strobe

SC010 491 G8 -16368 Any-key-down flag and Clear-strobe switch

Hexadecimal refers to the base-16
number system, which uses the ten
digits through 9 and the six letters A
through F to represent values from
to 15.

Your programs can get the code for the last key pressed by
reading the keyboard-data location. Table 2-2 gives this location
in three different forms: the hexadecimal value used in assembly
language, indicated by a preceeding dollar sign ($); the decimal
value used in Applesoft BASIC, and the complementary decimal
value used in Apple Integer BASIC. (Integer BASIC requires that
values greater than 32767 be written as the number obtained by
subtracting 65536 from the value. These are the decimal
numbers shown as negative in the tables; refer to the Apple II
BASIC Programming Manual.) The low-order seven bits of the
byte at the keyboard location contain the character code; the
high-order bit of this byte is the strobe bit, described below.

The Keyboard

location. This location is a combination flag and switch; the flag
tells whether any key is down, and the switch clears the strobe
bit. The switch function of this memory location is called a soft
switch because it is controlled by software. In this case, it
doesn't matter whether the program reads or writes, and it
doesn't matter what data the program writes: the only action that
occurs is the resetting of the keyboard strobe. Similar soft
switches, described later, are used for controlling other functions
in the Apple Me.

Any time you read the Any-key-down flag, you also clear the
keyboard strobe. If your program needs to read both the flag and
the strobe, it must read the strobe bit first.

Table 2-3b Keys and ASCII Codes,
continued

Codes are shown here in hexadecimal;
to find the decimal equivalents, use
Table 2-4.

Key

Normal

Control

Shift

Both

— i

]}

» ~_.

X
Y

■4

The Keyboard

Table 2-4 The ASCII Character Set

After the keyboard strobe has been cleared, it remains low until
another key is pressed. Even after you have cleared the strobe,
you can still read the character code at the keyboard location.
The data byte has a different value, because the high-order bit is
no longer set, but the ASCII code in the seven low-order bits is
the same until another key is pressed. Tables 2-3a and 2-3b
show the ASCII codes for most of the keys on the keyboard of
the Apple lie.

Dec Hex Char

Dec Hex Char !«■

00 NUL

1 01 SOH

2 02 STX

3 03 ETX

4 04 EOT

5 05 ENQ

6 06 ACK

7 07 BEL

8 08 BS

9 09 HT

10 0A LF

11 0B VT

12 0C FF

13 0D CR

14 OE SO

15 OF SI

16 10 DLE

17 11 DC1

18 12 DC2

19 13 DC3

20 14 DC4

21 15 NAK

22 16 SYN

23 17 ETB

24 18 CAN

25 19 EM

26 1A SUB

27 1 B ESC

28 1C fd

29 1D GS

30 1 E RS

31 1F US

32 20 SP

33 21 !

34 22 "

35 23 #

36 24 $

37 25 %

38 26 &

39 27

40 28 (

41 29 )

42 2A

43 2B +

44 2C

45 2D

46 2E

47 2F /

48 30

49 31 1

50 32 2

51 33 3

52 34 4

53 35 5

54 36 6

55 37 7

56 38 8

57 39 9

58 3A

59 3B ;

60 3C <

61 3D

62 3E >

63 3F ?

[

]

96 60

97 61 a

98 62 b

99 63 c

100 64 d

101 65 e

1 02 66 f

1 03 67 g

1 04 68 h

105 69 i

1 06 6A j

107 6B k

108 6C I

109 6D m

110 6E n

111 6F o

112 70 p

113 71 q

114 72 r

115 73 s

116 74 t

117 75 u

118 76 v

119 77 w

120 78 x

121 79 y

122 7A z

123 7B {

124 7C |

125 7D }

126 7E

127 7F DEL

Built-in I/O Devices

There are several special-function keys that do not gene rate
ASC IIcodes.Fore xample.youcannotreadthel CONTROL! , | SHIFT
and |CftPS lock] keys directly, but pressing one of these keys
alters the character codes produced by the other keys.

Another key that doesn't generate a code is the | RESET j key,
located at the upper-right corner of the keyboard; it is connected
dire ctly to the A pple lie's circuits. Pressing the | RESET | key with
the | control 1 key depressed normally causes the system to stop
whatever program it's running and restart itself. This restarting
process is called the reset routine, and it is described in
Chapter 4.

Two more special keys are marked with two versions of the
Apple logo and located on either side of the space bar. The key
with the outlined apple is the | open-apple 1 key; the key with the
solid-color apple is the | SOLlD-ftPPLE | key. These keys are
connected to the one-bit game inputs, which are described later
in th is chapte r. Pressing them in combination with the [ control]
and | RESET | keys causes the built-in firmware to perform special
reset and self-test cycles, described with the reset routine in
Chapter 4.

The Video Display Generator

The primary output device of the Apple lie is the video display.
You can use any ordinary video monitor, either color or black-
and-white, to display video information from the Apple Me. An
ordinary monitor is one that accepts composite video compatible
with the standard set by the NTSC (National Television
Standards Committee). If you use Apple lie color graphics with a
black-and-white monitor, the display will appear as different
shades of gray.

If you are only using 40-column text and graphics modes, you
can use a television set for your video display. If the TV set has
an input connector for composite video, you can connect it
directly to your Apple lie; if it does not, you'll need to attach an
RF video modulator between the Apple lie and the television set.

With the 80-column text card installed, the Apple Me can produce an
80-column text display. However, if you use an ordinary color or
black-and-white television set, 80-column text will be too blurry to
read. For a clear 80-column display, you must use a high-resolution
video monitor with a bandwidth of 1 4 MHz or greater.

The Video Display Generator

The specifications for the video display are summarized in
Table 2-5.

Table 2-5 Video Display Display modes: 40-column text

Specifications 80-column text with optional card

Low-resolution color graphics
High-resolution color graphics

Text capacity: 24 lines by 40 columns

24 lines by 80 columns with
optional card

Character set: 96 ASCII characters

(uppercase and lowercase)

Display formats: Normal, Inverse, Flashing

Low-resolution graphics: 16 colors, 40 horizontal by
48 vertical

High-resolution graphics: 6 colors, 280 horizontal by
192 vertical

The video signal produced by the Apple lie is NTSC-compatible
composite color video. It is available at three places: the RCA-
type phono jack on the back of the Apple Me, the single Molex-
type pin on the main circuit board near the back on the right
side, and one of the group of four Molex-type pins in the same
area on the main board. Use the RCA-type phono jack to
connect a video monitor or an external video modulator; use the
Molex pins to connect the type of video modulator that fits inside
the Apple lie case. For a full description of the video signal and
the connections to the Molex-type pins, refer to the section
"Video Output Signals" in Chapter 7.

The Apple Me can produce four different kinds of video display:

• Text, 24 lines of 40 characters

• Text, 24 lines of 80 characters (with optional card)

• Low-resolution graphics, 40 by 48, in 1 6 colors

• High-resolution graphics, 280 by 192, in 6 colors

Built-in I/O Devices

Either of the two text modes can display all 96 ASCII characters:
the upper- and lowercase letters, numbers, and symbols.

Either of the graphics displays can have four lines of text, either
40-column or 80-column, at the bottom of the screen. Graphics
displays with text at the bottom are called mixed-mode displays.

The low-resolution graphics display is an array of colored blocks,
40 wide by 48 high, in any of sixteen colors. In mixed mode, the
four lines of text replace the bottom eight rows of blocks, leaving
40 rows of 40 blocks each.

The high-resolution graphics display is an array of dots, 280 wide
by 192 high. There are six colors available in high-resolution
displays, but a given dot can only use four of the six colors. In
mixed mode, the four lines of text replace the bottom 32 rows of
dots, leaving 160 rows of 280 dots each.

Text Modes

The text characters displayed include the upper- and lowercase
letters, the ten digits, punctuation marks, and special characters.
Each character is displayed in an area of the screen that is
seven dots wide by eight dots high. The characters are formed
by a dot matrix five dots wide, leaving two blank columns of dots
between characters in a row. Except for lowercase letters with
descenders, the characters are only seven dots high, leaving one
blank line of dots between rows of characters.

The normal display has white (or other single color) dots on a
black background. Characters can also be displayed as black
dots on a white background; this is called inverse format.

Text Character Sets

The Apple lie can display either of two text character sets: the
primary set or an alternate set. The forms of the characters in
the two sets are actually the same, but the available display
formats are different. The display formats are

• normal, with white dots on a black screen;

• inverse, with black dots on a white screen; and

• flashing, alternating between normal and inverse.

The Video Display Generator

With the primary character set, the Apple He can display
uppercase characters in all three formats: normal, inverse, and
flashing. Lowercase letters can only be displayed in normal
format. The primary character set is compatible with most
software written for the Apple II and Apple II Plus models, which
can display text in flashing format but don't have lowercase
characters.

The alternate character set sacrifices the flashing format for a
complete inverse format. With the alternate character set, the
Apple He can display uppercase letters, lowercase letters,
numbers, and special characters in either normal format or
inverse format.

You select the character set by means of the alternate-text soft
switch, described below in the section "Display Mode Switching".
Table 2-6 shows the character codes in decimal and hexadecimal
for the Apple lie primary and alternate character sets in normal,
inverse, and flashing formats.

Table 2-6 The Display Character Sets

To identify particular characters and
values, refer to Table 2-4.

Primary Character Set:
Hex Values Character Type Format

Alternate Character Set:
Character Type Format

$00-$1 F

Uppercase letters

Inverse

Uppercase letters

Inverse

$20-$3F

Special characters

Inverse

Special characters

Inverse

$40-$5F

Uppercase letters

Flashing

Uppercase letters

Inverse

$60-$7F

Special characters

Flashing

Lowercase letters

Inverse

$80-$9F

Uppercase letters

Normal

Uppercase letters

Normal

$A0-$BF

Special characters

Normal

Special characters

Normal

$CO-$DF

Uppercase letters

Normal

Uppercase letters

Normal

$EO-$FF

Lowercase letters

Normal

Lowercase letters

Normal

Built-in I/O Devices

Each character on the screen is stored as one byte of display
data. The low-order six bits make up the ASCII code of the
character being displayed. The remaining two (high-order) bits
select inverse or flashing format and uppercase or lowercase
characters. In the primary character set, bit 7 selects inverse or
normal format and bit 6 controls character flashing. In the
alternate character set, bit 6 selects between upper- and
lowercase, according to the ASCII character codes, and flashing
format is not available.

40-column versus 80-column Text

The Apple Me has two modes of text display: 40-column and 80-
column. (The 80-column display mode described in this manual is
the one you get with the 80-column text card or other auxiliary-
memory card installed in the auxiliary slot.) The number of dots
in each character does not change, but the characters in 80-
column mode are only half as wide as the characters in 40-
column mode. Compare Figure 2-2 and Figure 2-3. On an
ordinary color or black-and-white television set, the narrow
characters in the 80-column display blur together; you must use
the 40-column mode to display text on a television set.

Figure 2-2 40-column Text Display

The Video Display Generator

Figure 2-3 80-column Text Display

Graphics Modes

The Apple Me can produce video graphics in either of two
different modes. Both graphics modes treat the screen as a
rectangular array of spots. Normally, your programs will use the
features of some high-level language to draw graphics dots,
lines, and shapes in these arrays; this section describes the way
the resulting graphics data are stored in the Apple lie's memory.

Low-resolution Graphics

In the low-resolution graphics mode, the Apple lie displays an
array of 48 rows by 40 columns of colored blocks. Each block
can be any one of sixteen colors, including black and white. On
a black-and-white monitor or television set, these colors appear
as black, white, and three shades of gray. There are no blank
dots between blocks; adjacent blocks of the same color merge to
make a larger shape.

Data for the low-resolution graphics display is stored in the same
part of memory as the data for the 40-column text display. Each
byte contains data for two low-resolution graphics blocks. The
two blocks are displayed one atop the other in a display space
the same size as a 40-column text character, seven dots wide by
eight dots high.

Half a byte — four bits, or one nybble — is assigned to each
graphics block. Each nybble can have a value from to 15, and
this value determines which one of sixteen colors appears on the

Built-in I/O Devices

screen. The colors and their corresponding nybble values are
shown in Table 2-7. In each byte, the low-order nybble sets the
color for the top block of the pair, and the high-order nybble sets
the color for the bottom block. Thus, a byte containing the
hexadecimal value $D8 produces a brown block atop a yellow
block on the screen.

Table 2-7 Low-resolution Graphics

Nybble

Value

Color

Nybble

Value

Color

Colors

Decimal

Hex

Decimal

Hex

Colors may vary, depending upon the

controls on the monitor or television

Black

Brown

set.

Magenta

Orange

Dark Blue

Grey 2

Purple

Pink

Dark Green

Light Green

Grey 1

Yellow

Medium Blue

Aquamarine

Light Blue

White

As explained below in the section "Display Pages", the text
display and the low-resolution graphics display use the same
area in memory. Most programs that generate text and graphics
clear this part of memory when they change display modes, but it
is possible to store data as text and display it as graphics, or
vice-versa. All you have to do is change the mode switch,
described in the section "Display Mode Switching", without
changing the display data. This usually produces meaningless
jumbles on the display, but some programs have used this
technique to good advantage for producing complex low-
resolution graphics displays quickly.

High-resolution Graphics

In the high-resolution graphics mode, the Apple Me displays an
array of colored dots in 192 rows and 280 columns. The colors /
available are black, white, purple, green, orange, and blue,
although the colors of the individual dots are limited, as
described below. Adjacent dots of the same color merge to form
a larger colored area.

The Video Display Generator

Data for the high-resolution graphics displays are stored in either
of two 8192-byte areas in memory. These areas are called high-
resolution Page 1 and Page 2; think of them as buffers where
you can put data to be displayed. Normally, your programs will
use the features of some high-level language to draw graphics
dots, lines, and shapes to display; this section describes the way
the resulting graphics data are stored in the Apple lie's memory.

The Apple lie high-resolution graphics display is bit-mapped: each
dot on the screen corresponds to a bit in the Apple lie's memory.
The seven low-order bits of each display byte control a row of
seven adjacent dots on the screen, and forty adjacent bytes in
memory control a row of 280 (7 times 40) dots. The least
significant bit of each byte is displayed as the leftmost dot in a
row of seven, followed by the second-least significant bit, and so
on, as shown in Figure 2-4. The eighth bit (the most significant)
of each byte is not displayed; it selects one of two color sets, as
described below.

On a black-and-white monitor, there is a simple correspondence
between bits in memory and dots on the screen. A dot is white if
the bit controlling it is on (1), and the dot is black if the bit is off
(0). On a black-and-white television set, pairs of dots blur
together; alternating black and white dots merge to a continuous
grey.

On an NTSC color monitor or a color television set, a dot whose
controlling bit is off (0) is black. If the bit is on, the dot will be
white or a color, depending on its position, the dots on either
side, and the setting of the high-order bit of the byte. Call the
left-most column of dots column zero, and assume (for the
moment) that the high-order bits of all the data bytes are off (0).
If the bits that control them are on, dots in even-numbered
columns, 0, 2, 4, and so forth, are purple, and dots in odd-
numbered columns are green — but only if the dots on either
side are black. If two adjacent dots are both on, they are both
white.

You select the other two colors, blue and orange, by turning the
high-order bit (bit 7) of a data byte on (1). The colored dots
controlled by a byte with the high-order bit on are either blue or
orange: the dots in even-numbered columns are blue, and the
dots in odd-numbered columns are orange — again, only if the
dots on either side are black. Within each horizontal line of seven
dots controlled by a single byte, you can have black, white, and

24 Built-in I/O Devices

one pair of colors. To change the color of any dot to one of the
other pair of colors, you must change the high-order bit of its
byte, which affects the colors of all seven dots controlled by the
byte.

In other words, high-resolution graphics displayed on a color
monitor or television set are made up of colored dots, according
to the following rules:

• Dots in even columns can be black, purple, or blue.

• Dots in odd columns can be black, green, or orange.

• If adjacent dots in a row are both on, they are both white.

• The colors in each row of seven dots controlled by a single
byte are either purple and green, or blue and orange,
depending on whether the high-order bit is off (0) or on (1).

These rules are summarized in Table 2-8. The blacks and whites
are numbered to remind you that the high-order bit is different.

Table 2-8 High-resolution Graphics

Bits 0-6

Bit 7 Off

Bit 7 On

Colors

Colors may vary, depending on the

Adjacent columns off

Black 1

Black 2

adjustment of the monitor or television

Even columns on

Purple

Blue

set.

Odd columns on

Green

Orange

Adjacent columns on

White 1

White 2

Figure 2-4 High-resolution Display Bits
Bits in Data Byte

The peculiar behavior of the high-resolution colors reflects the
way NTSC color television works. The dots that make up the
Apple Me video signal are spaced to coincide with the frequency
of the color subcarrier used in the NTSC system. Alternating
black and white dots at this spacing cause a color monitor or TV
set to produce color, but two or more white dots together do not.
For more details about the way the Apple Me produces color on a
TV set, see Chapter 7. For information about the way NTSC
color television works, see the magazine articles listed in the
bibliography.

Dots on Graphics Screen

The Video Display Generator

Display Pages

The Apple lie generates its video displays using data stored in
specific areas in memory. These areas, called display pages,
serve as buffers where your programs can put data to be
displayed. Each byte in a display buffer controls an object at a
certain location on the display. In text mode, the object is a
single character; in low-resolution graphics, the object is two
stacked colored blocks; and in high-resolution mode, it is a line
of seven adjacent dots.

The 40-column-text and low-resolution-graphics modes use two
display pages of 1024 bytes each. These are called text Page 1
and Text Page 2, and they are located at 1 024-2047 (hexadecimal
$400-$7FF)and2048-307l ($80 0-$BFF) in main memory. Normally,
only Page 1 is used, but you can put text or graphics data into
Page 2 and switch displays instantly. Either page can be
displayed as 40ycolumn text, low-resolution graphics, or mixed-
mode (four rows of text at the bottom of a graphics display).

The 80-column text mode displays twice as much data as the
40-column mode — 1920 bytes — but it cannot switch pages. The
80-column text display uses a combination page made up of text
Page 1 in main memory plus another page in auxiliary memory
located on the 80-column text card. This additional memory is NOT
the same as text Page 2 — in fact, it occupies the same address
space as text Page 1 , and there is a special soft switch that enables
you to store data into it (see the section "Display Mode Switching",
below). The built-in firmware I/O routines described in Chapter 3
take care of this extra addressing automatically; that is one reason
to use those routines for all your normal text output.

The high-resolution graphics mode also has two display pages,
but each page is 8192 bytes long. In the 40-column text and low-
resolution graphics modes each byte controls a display area
seven dots wide by eight dots high. In high-resolution graphics
mode each byte controls an area seven dots wide by one dot
high. Thus, a high-resolution display requires eight times as
much data storage, as shown in Table 2-9.

Built-in I/O Devices

Table 2-9 Video Display Page
Locations

*Note: 80-column mode uses the
1024-byte page-1 locations in both
main and auxiliary memory. The
PAGE 2 switch is used to select one
or the other for storing data (see the
section "Display Mode Switching").

Display mode

Page

Lowest
Address

Highest
Address

40-column Text,

Low-resolution

Graphics

1
2

MOO
*800

1024
2048

$7FF 2047
*BFF 3071

80-column Text

*400

1 024

$7FF 2047

High-resolution

$2000

8192

$3FFF

1B383

Graphics

$4000

16384

$5FFF

24575

Display Mode Switching

You select the disptay^mode that is appropriate for your
application by reading or writing to a reserved memory location
called a soft switch. In the Apple lie, most soft switches have
three memory locations reserved for them: one for turning the
switch on, one for turning it off, and one for reading the current
state of the switch.

Table 2-10 shows the reserved locations for the soft switches
that control the different display modes. For example, to switch
from mixed-mode to full-screen graphics in an assembly-language
program, you could use the instruction:

STA $C052

To do this in a BASIC program, you could use the instruction:

POKE 49234,0

The table gives the switch locations in three forms: hexadecimal,
decimal, and negative decimal. You can use the hexadecimal
values in your machine-language programs. Use the decimal
values in PEEK or POKE commands in Applesoft BASIC; the
negative values are for Integer BASIC.

You may not need to deal with these functions by reading and
writing directly to the memory locations in this table. Many of the
functions shown here are selected automatically if you use the
display routines in the various high-level languages on the Apple lie.

The Video Display Generator

Some of the soft switches in Table 2-10 are marked read or
write. Those soft switches share their locations with the keyboard
data and strobe functions. In the original Apple II, memory
locations from $ c o o to * c o 1 F (491 52 to 491 83) were used only for
the keyboard data and strobe functions. In the Apple lie, these
locations are used the same way, but only when you read to get
data and write to clear the strobe. To perform the function shown
in the table, use the operation listed there. Soft switches that are
not marked may be accessed by either a read or a write. When
writing to a soft switch, it doesn't matter what value you write;
the action occurs when you address the location, and the value
is ignored.

Table 2-10 Display Soft Switches

(1 ) This mode is only effective when
graphics-mode switch is ON.

(2) This switch has a different function
when the 80-column text card's
auxiliary text page is enabled for
writing. Refer to the next section,
"Addressing Display Pages Directly ".

(3) This switch changes the function of
the PAGE2 switch for addressing the
auxiliary text memory on the extended
80-column text card. The next section
describes how to do this.

(4) Reading this location returns the
state of the vertical blanking
signal VBL . The function of VBL is
described in Chapter 7 in the section
"Video Output Signals."

Name

Function

Hex

Location
Decimal

Notes

ALTCHARSET

Alternate char, set on
Alternate char, set off
Read ALTCHARSET switch

*C00F 49167 -16369 Write
*C00E 49166 -16370 Write
*C01E 49182 -16354 Read

TEXT

Text mode on

Text mode off (graphics)

Read TEXT switch

SC051
*C050
*C01 A

49233
49232
49178

-16303
-16304
-16358

Read

MIXED

Mixed-mode on
Mixed-mode off
Read MIXED switch

*C053
$C052
*C01B

49235
49234
49179

-16301
-16302
-16357

1
1
Read

PAGE2

Page 2 on

Page 2 off (Page 1 )

Read PAGE 2 switch

*C055
*C054
*C01C

49237
49236
49180

-16299
-16300
-16356

2
2
Read

HIRES

Hi-res mode on
Hi-res mode off
Read HIRES switch

$C057
$C056
*C01D

49239
49238
49181

-16297
-16298
-16355

1
1
Read

80C0L

80-column display on
80-column display off
Read 80C0L switch

*C00D
$C00C
$C01F

49165
49164
49183

-16371
-16372
-16353

Write
Write
Read

80 STORE Store in auxiliary memory

Store in main memory
Read 80STORE switch

$C001 49153 -16383 Write, 3
*COO0 49152 -16384 Write, 3
$C018 49176 -16360 Read

VBL

Read vertical blanking

*C019 49177 -16359 Read, 4

Built-in I/O Devices

Any time you read a soft switch, you get a byte of data.
However, the only information the byte contains is the state of
the switch, and this occupies only one bit — bit 7, the high-order
bit. The other bits in the byte are unpredictable. If you are
programming in machine language, the switch setting is the sign
bit; as soon as you read the byte, you can do a Branch Plus if
the switch is off, or Branch Minus if the switch if on.

If you read a soft-switch from a BASIC program, you get a value
between and 255. Bit 7 has a value of 128, so if the switch is
on, the value will be equal to or greater than 128; if the switch is
off, the value will be less than 128.

Addressing Display Pages Directly

Before you decide to use the display pages directly, consider the
alternatives. Most high-level languages enable you to write
statements that control the text and graphics displays. Similarly, if
you are programming in assembly language, you may be able to
use the display features of the built-in I/O firmware. You should
store directly into display memory only if the existing programs
can't meet your requirements.

The display memory maps are shown in Figures 2-5, 2-6, 2-7,
and 2-8. All of the different display modes use the same basic
addressing scheme: characters or graphics bytes are stored as
rows of 40 contiguous bytes, but the rows themselves are not
stored at locations corresponding to their locations on the display.
Instead, the display address is transformed so that three rows
that are eight rows apart on the display are grouped together and
stored in the first 120 locations of each block of 128 bytes ($80
hexadecimal). By folding the display data into memory this way,
the Apple lie, like the Apple II, stores all 960 characters of
displayed text within 1 K bytes of memory. For a full description of
the way the Apple lie handles its display memory, refer to the
section "Display Memory Addressing" in Chapter 7.

The high-resolution graphics display is stored in much the same
way as text, but there are eight times as many bytes to store,
because eight rows of dots occupy the same space on the
display as one row of characters. The subset consisting of all the
first rows from the groups of eight is stored in the first 1024
bytes of the high-resolution display page. The subset consisting
of all the second rows from the groups of eight is stored in the
second 1024 bytes, and so on for a total of 8 times 1024, or

The Video Display Generator 29

_ _ _

8192 bytes. In other words, each block of 1024 bytes In the high-
resolution display page contains one row of dots out of every
group of eight rows. The individual rows are stored in sets of
three forty-byte rows, the same way as the text display.

All of the display modes except 80-column mode can use either
of two display pages. The display maps show addresses only for
each Page 1. To obtain addresses for text or low-resolution
graphics Page 2, add 1024 ($400); to obtain addresses for high-
resolution Page 2, add 8192 ($2000).

The 80-column display works a little differently. Half of the data is
stored in the normal text Page-1 memory, and the other half is
stored in memory on the 80-column text carcfusTng the same
addresses. The display circuitry fetches bytes from these two
memory areas simultaneously and displays them sequentially:
first the byte from the 80-column text card memory, then the byte
from the main memory. The main memory stores the characters
in the odd columns of the display, and the 80-column text card
memory stores the characters in the even columns.

To store display data on the 80-column text card, first turn on the
80STORE Softswitch by writing to location 491 53 (hexadecimal *C001
or complementary - 1 6383). With 80STORE on, the page-select switch
PAGE2 selects between the portion of the 80-column display stored
in Page 1 of main memory and the portion stored in the 80-
column text card memory. To select the 80-column text card, turn
the PAGE2 soft switch on by reading or writing at location 49237.
For more details about the way the displays are generated, see
Chapter 7.

30 Built-in I/O Devices

Figure 2-5 Map of 40-column Text
Display

wn^mtoNcofl><aiOD

ooooooooooooooo.

$400

$480

$500

$580

$600

$680

$700

$780

$428

$4A8

$528

$5A8

$628

$6A8

$728

$7A8

$450

$400

$550

$5D0

$650

$6D0

$750

$7D0

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1280

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1960

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1232

1360

1488

1616

1744

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2000

The Video Display Generator

Figure 2-6 Map of 80-column Text
Display

MAIN

MEMORY

AUXILIARY

MEMORY

$400

1024

$480

1152

$500

1280

$580

1408

$600

1536

$680

1664

$700

1792

$780

1920

$428

1064

$4A8

1192

$528

1320

$5A8

1448

$628

1576

$6A8

1704

$728

1832

$7A8

1960

$450

1104

$4D0

1232

$550

1360

$5D0

1488

$650

1616

$6D0

1744

$750

1872

$7D0

2000

$00 $01 $02 $03 $04 $05 $06
12 3 4 5 6

$00 $01 $02 $03 $04 $05 $06 $07
1 2 3 4 5 6 7

$49 $4A $4B $4C $4D $4E $4F
73 74 75 76 77 78 79

$49
73

$4A
74

$4E
75

$4C
76

64D

54E
78

54F
79

)

(

)

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)

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Built-in I/O Devices

Figure 2-7 Map of Low-resolution
Graphics Display

.~d

$400

$480

$500

$580

$600

$680

$700

$780

$428

$4A8

$528

$5A8

$628

$6A8

$728

$7A8

$450

$4D0

$550

$5D0

$650

$6D0

$750

$7D0

r*»

CM
C\J

CO
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CD
CM

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CO

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1024

1 152

1280

1408

1536

1664

1792

1920

1064

1 192

1320

1448

1576

1704

1832

1960

1 104

1232

1360

1616

1 744

2000

....

The Video Display Generator

Figure 2-8 Map of High-resolution
Graphics Display

$2000
$2080
$2100
$2180
$2200
$2280
$2300
$2380
$2028
$20A8
$2128
$21 A8
$2228
$22A8
$2328
$23A8
$2050
$20D0
$2150
$21 DO
$2250
$22D0
$2350
$23D0

o^cMn9inioNa)o)<mOQujiLO^wco^m(Oscoo)<a)OQiuii.O'-wp)'tu)(Ds

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CD
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8832

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9088

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8488

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8872

$0000

9000

1024 $0400

9128

8272

2048 $0800

8400

8528

3072 $0C00

8656

8784

4096 $1000

— i

8912

5120 $1400

9040

9168

6144 $1800

7168 $1C00

Built-in I/O Devices

Secondary Inputs and Outputs

In addition to the primary I/O devices — the keyboard and
display — there are several secondary input and output devices
in the Apple He. These devices are

The speaker (output)

Cassette input and output

Annunciator outputs

Strobe output

Switch inputs

Analog (hand control) inputs .

These devices are similar in operation to the soft switches
described in the previous section: you control them by reading or
writing to dedicated memory locations. Action takes place any
time your program reads or writes to one of these locations;
information written is ignored.

Some of these devices toggle — change state — each time they
are accessed. If you write using an indexed store operation, the
Apple lie's 6502 microprocessor activates the address bus twice
during successive clock cycles, causing a device that toggles each
time it is addressed to end up back in its original state. For this
reason, you should read, rather than write, to such devices.

The Speaker

The Apple Me has a small speaker mounted toward the front of
the bottom plate. The speaker is connected to a soft switch that
toggles; it has two states, off and on, and it changes from one to
the other each time it is accessed. Electrical specifications of the
speaker circuit appear in Chapter 7.

If you switch the speaker once, it emits a click; to make longer
sounds, you access the speaker repeatedly. You should always
use a read operation to toggle the speaker. If you write to this
soft switch, it switches twice in rapid succession. The resulting
pulse is so short that the speaker doesn't have time to respond;
it doesn't make a sound.

The soft switch for the speaker uses memory location 49200
(hexadecimal $C030). From Integer BASIC, use the complementary
address -1 6336. You can make various tones and buzzes with the

Secondary Inputs and Outputs 35

speaker by using combinations of timing loops in your program.
There is also a routine in the built-in firmware to make a beep
through the speaker. This routine is called belli ; it is described in
Appendix C.

Cassette Input and Output

There are two miniature phone jacks on the back panel of the
Apple lie. You can use a pair of standard cables with miniature
phone plugs to connect an ordinary cassette tape recorder to the
Apple Me and save programs and data on audio cassettes.

The phone jack marked with a picture of an arrow poinding
towards a cassette is the output jack. It is connected to a toggled
soft switch, like the speaker switch described above. The signal
at the phone jack switches from zero to 25 millivolts or from 25
millivolts to zero each time you access the soft switch. Detailed
electrical specifications for the cassette input and output are
given in Chapter 7.

If you connect a cable from this jack to the microphone input of a
cassette tape recorder and switch the recorder to record mode,
the signal changes you produce by accessing this soft switch will
be recorded on the tape. The cassette output switch uses
memory location 49184 (hexadecimal *C020; complementary value
-1 G352). Like the speaker, this output will toggle twice if you write
to it, so you should only use read operations to control the
cassette output.

The standard method for writing computer data on audio tapes
uses tones with two different pitches to represent the binary
states zero and one. To store data, you convert the data into a
stream of bits, and convert the bits into the appropriate tones. To
save you the trouble of actually programming the tones, and to
ensure consistency among all Apple II cassette tapes, there is a
built-in routine for producing cassette data output. This routine,
called NRITE, is described in Appendix C.

The phone jack marked with a picture of an arrow coming from a
cassette is the input jack. It accepts a cable from the cassette
recorder's earphone jack. The signal from the cassette is 1 volt
(peak-to-peak) audio. Each time the instantaneous value of this
audio signal changes from positive to negative, or vice-versa, the
state of the cassette input circuit changes from zero to one or
vice-versa. You can read the state of this circuit at memory
location 49248 (hexadecimal $C060, or complementary decimal

-16288).

Built-in I/O Devices

When you read this location, you get a byte, but only the high-
order bit (bit 7) is valid. If you are programming in machine
language, this is the sign bit, so you can perform a Branch Plus
or Branch Minus immediately after reading this byte. BASIC is
too slow to keep up with the audio tones used for data recording
on tape, but you don't need to write the program: there is a built-
in routine for reading data from a cassette. It is called READ, and it
is described in Appendix C.

The Hand Control Connector Signals

Several inputs are available on a 9-pin D-type miniature
connector on the back of the Apple He: three one-bit inputs, or
switches, and four analog inputs. These signals are also
available on the sixteen-pin IC connector on the main circuit
board, along with four one-bit outputsjind a data strobe. You can
access all of these signals from your programs.

Ordinarily, you connect a pair of hand controls to the 9-pin
connector. The rotary controls use two analog inputs, and the
push-buttons use two one-bit inputs. However, you can also use
these inputs and outputs for many other jobs. For example, two
analog inputs can be used with a two-axis joystick. Complete
electrical specifications of these inputs and outputs are given in
Chapter 7; Table 7-18 shows the connector pin numbers.

Annunciator Outputs

The four one-bit outputs are called annunciators. Each
annunciator can be used to turn a lamp, a relay, or some similar
electronic device on and off. For electrical specifications of the
annunciator outputs, refer to Chapter 7.

Each annunciator is controlled by a soft switch, and each switch
uses a pair of memory locations. These memory locations are
shown in Table 2-1 1 . Any reference to the first location of a pair
turns the corresponding annunciator off; a reference to the
second location turns the annunciator on. There is no way to
read the state of an annunciator.

Secondary Inputs and Outputs 37

Table 2-11 Annunciator Memory
Locations

*Pin numbers given are for the 16-pin
IC connector on the circuit board.

No.

Annunciator
Pin*

State

Address
Decimal

Hex

off
on

49240
49241

-16296
-16295

«C0S8
*C059

off

49242
49243

-16294
-16293

*C05A
ICOSB

off
on

49244
49245

-16292
-16291

JC05C
*C05D

off
on

4924G
49247

-16290
-16289

SC05E
$C05F

Strobe Output

The strobe output is normally at +5 volts, but it drops to zero for
about half a microsecond any time its dedicated memory location
is accessed. You can use this signal to control functions such as
data latching in external devices. If you use this signal,
remember that memory is addressed twice by a write; if you
need only a single pulse, use a read operation to activate the
strobe. The memory location for the strobe signal is 4921 6
(hexadecimal $C040 or complementary -16320).

Switch Inputs

The three one-bit inputs can be connected to the output of
another electronic device or to a pushbutton. When you read a
byte from one of these locations, only the high-order bit — bit
7 — is valid information; the rest of the byte is undefined. From
machine language, you can do a Branch Plus or Branch Minus
on the state of bit 7. From BASIC, you read the switch with a
PEEK and compare the value with 128. If the value is 128 or
greater, the switch is on.

The memory locations for these switches are 49249 through
49251 (hexadecimal $C061 through $C063, orcomplementary
-16287 through -16285), as shown in Table 2-12. Switch
and switch 1 are permanently connected to the I OPEN-APPLE [ and
\ SO LID-APP LET] keys on the keyboard; these are the ones normally
connected to the buttons on the hand controls. Some software
for the older models of the Apple II uses the third switch, switch

Built-in I/O Devices

2, as a way of detecting the shift key. This technique requires a
hardware modification known as the single-wire shift-key mod.

To perform this modification on your Apple He, all you have to do is
solder across the broken circle labelled X6 on the main circuit board.
Early production Apple lies, identified by a circuit board part number
ending in -A, have the shift-key mod active; you can remove it by
breaking the circuit at X6. Remember to turn off the power before
changing anything inside the Apple lie. Also remember that changes
such as this are at your own risk and may void the warranty.

Warning

If you make the shift-key modification and connect a joystick or
other hand control that uses s witch 2 you must be careful never to
close the switch and press the |smFT| key at the same time: doing
this produces a short circuit that causes the power supply to turn
off. When this happens, any programs or data in the computer's
internal memory are lost.

Analog Inputs

The four analog inputs are designed for use with 150K ohm
variable resistors or potentiometers. The variable resistance is
connected between the +5V supply and each input, so that it
makes up part of a timing circuit (refer to Chapter 7 for details).
The circuit changes state when its time constant has elapsed,
and the time constant varies as the resistance varies. Your
program can measure this time by counting in a loop until the
circuit changes state, or times out.

Before a program can read the analog inputs, it must first reset
the timing circuits. Accessing memory location 49264 (hexadecimal
$C070 or complementary -16272) does this. As soon as you reset
the timing circuits, the high bits of the bytes at locations 49252
through 49255 (hexadecimal$C064through$C067orcomplementary
-1 6284 through -1 6281 ) are set to one. If you peek at them from
BASIC, the values will be 128 or greater. Within about 3
milliseconds, these bits will change back to zero — byte values
less than 128 — and remain there until you reset the timing
circuits again. The exact time each of the four bits remains high
is directly proportional to the resistance connected to the
corresponding input. If these inputs are open — no resistances
are connected — the corresponding bits may remain high
indefinitely.

To read the analog inputs from machine language, you can use
a program loop that resets the timers and then increments a
counter until the bit at the appropriate memory location changes

Secondary Inputs and Outputs 39

to zero, or you can use the built-in routine. It is called PREAD, and
it is described in Appendix C. BASIC and other high-level
languages also include convenient means of reading the analog
inputs: refer to your language manuals.

Summary of Secondary I/O Locations

Table 2-12 shows the memory locations for all of the built-in I/O
devices except the keyboard and display. As explained above,
some soft switches should only be accessed by means of read
operations; those switches are marked.

Table 2-12 Secondary I/O Memory
Locations

Function

Address
■^"^ Decimal Hex

Notes

For connector identification and pin
numbers, refer to Tables 7-1 7 and
7-18.

Speaker

49200

-16336

$C030

Read

Cassette Out
Cassette In

49184
49248

-16352
-16288

$C020
$C060

Read
Read

Annunciator On
Annunciator Off

49241
49240

-16295
-16296

SC059
$C058

Annunciator 1 On
Annunciator 1 Off

49243
49242

-16293
-16294

*C05B
$C0SA

Annunciator 2 On
Annunciator 2 Off

49245
49244

-16291
-16292

*C05D
$C05C

Annunciator 3 On
Annunciator 3 Off

49247
49246

16289
-16290

*C05F
*C05E

Strobe Output

49216

-16320

$C040

Read

Switch Input

49249

-16287

*C061

Read

(|OPEN-APPLE| key)

Switch Input 1

49250

-16286

*C062

Read

(I SOLID-APPLE (key)

Switch Input 2

49251

-16285

$C063

Read

Analog Input Reset

49264

-16272

*C070

Analog Input
Analog Input 1
Analog Input 2
Analog Input 3

49252
49253
49254
49255

-16284
-16283
-16282
-16281

$C064
$C065
$C066
*C067

Read
Read
Read
Read

Built-in I/O Devices

Built-in 110 Firmware

44 Using the I/O Subroutines

44 Apple II Compatibility/

45 The 80-column Firmware
47 The Old Monitor

47 The Standard I/O Links

48 Standard Output Features
48 COUT Output Subroutine

50 Control Characters with COUT1

50 The Stop-List Feature

50 The Text Window

52 Inverse and Flashing Text

53 Standard Input Features

53 RDKEY Input Subroutine

54 KEYIN Input Subroutine

55 Escape Codes with KEYIN

56 Cursor Motion in Escape Mode
56 GETLN Input Subroutine

58 Editing with GETLN

58 Cancel Line

58 Backspace

58 Retype

Built-in I/O Firmware

fer - ^

-gui

Chapter 3

Built-in 110 Firmware

The Monitor, or System Monitor, is a
computer program that is used to
operate the computer at the machine
level.

Almost every program on the Apple lie takes input from the
keyboard and sends output to the display. The Monitor and the
Applesoft and Integer BASICS do this by means of standard I/O
subroutines that are built into the Apple lie's firmware. Many
applications programs also use the standard I/O subroutines, but
programs written in Pascal do not; Pascal has its own I/O
subroutines.

This chapter describes the features of these subroutines as they
are used by the Monitor and by the BASIC interpreters, and tells
you how to use the standard subroutines in your assembly-
language programs.

High-level languages already include convenient methods for
handling most of the functions described in this chapter. You should
not need to use the standard I/O subroutines in your programs
unless you are programming in assembly language.

Table 3-1 Standard I/O Subroutines

Subroutine
Name

Location

Description

CQUT $FDED Character Out: sends a character to the display.

RDKEY $FDQC Read Key: displays the blinking cursor; goes to the

standard input routine, normally KEY IN.

KEY IN *FD1B Key In: with 80-column firmware active, displays

checkerboard cursor. Accepts a character from the
keyboard.

GETLN SFDGA Get Line: displays the prompt character; accepts a

sequence of characters by means of RDKEY.

Built-in I/O Firmware

The standard I/O subroutines listed in Table 3-1 are fully
described in this chapter. The Apple Me firmware also contains
many other subroutines that you might find useful. Those
subroutines are described in Appendix C. Two of the built-in
subroutines, auxmove and xfer, can help you use the optional
auxiliary memory; those subroutines are described in Chapter 4.

Using the I/O Subroutines

Before you use the standard I/O subroutines, you should
understand a little about the way they are used. The Apple He
firmware operates differently with different options such as the
80-column text card. This section describes general situations
that affect the operation of the standard I/O subroutines. Specific
instances are described in the sections devoted to the individual
subroutines.

Table 3-2 Apple II Mode

Apple II Compatibility

Compared to older Apple II models, the Apple lie has some
additional keyboard and display features. To run programs that
were written for the older models, you can make the Apple lie
resemble an Apple II Plus by turning those features off. The
features that you can turn off and on to put the Apple Me into and
out of Apple II mode are listed in Table 3-2.

Apple He

Apple II Mode

Keyboard:

Uppercase and lowercase

Uppercase only

Display Characters:

Inverse and normal only

Flashing, inverse, and
normal

Display size:

40-column; also
80-column, with optional
card

40-column only

§j-

If the Apple Me does not have an 80-column text card installed in
the auxiliary slot, it is almost in Apple II mode as soon as you
turn it on or reset it. One exception is the keyboard, which is
both uppercase and lowercase. To be compatible with older
software, you have to switch the Apple Me keyboard to uppercase
by pressing the [~CftPS lock ] key.

litarf

Built-in I/O Firmware

Statements in App lesoft and Int eger BASIC must be typed in
uppercase letters. | CAPS lock] will take care of this, but it makes it
inconvenient to use lowercase letters in print statements. If the
80-column firmware is active (see below), you can use
uppercase-restrict mode, which forces typed letters to uppercase
except inside quotation marks (see Table 3-6).

Another feature that is different on the Apple He is the displayed
character set. Older Apple Ms display only uppercase characters,
but they display them three ways: normal, inverse, and flashing.
The Apple lie can display uppercase characters all three ways,
and it can display lowercase characters in the normal way. This
combination is called the primary character set. When the
Apple lie is first turned on or reset, it displays the primary
character set.

The Apple Me has another character set, called the alternate
character set, that displays a full set of normal and inverse
uppercase and lowercase characters, but can't display flashing
characters. The primary and alternate character sets are
described in Chapter 2. You can switch character sets at any
time by means of the ALTCHARSET soft switch, also described in
Chapter 2.

The 80-column Firmware

There are a few features that are normally available only with the
optional 80-column display. These features are identified in
Tables 3-3a and 3-3b and Table 3-6. The firmware that supports
these features is built into the Apple lie, but it is normally active
only if an 80-column text card is installed in the auxiliary slot.

When you turn on power or reset the Apple Me, the 80-column
firmware is inactive and the Apple Me displays the primary
character set, even if an 80-column text card is installed. When
you activate the 80-column firmware as described below, it
switches to the alternate character set.

The built-in 80-column firmware is implemented as if it were
installed in expansion slot 3. Programs written for older Apple lis
with 80-column display cards installed in slot 3 will run properly
on an Apple Me with an 80-column text card.

Using the I/O Subroutines

If the Apple lie has an 80-column text card and you want to use
the 80-column display, you can activate the built-in firmware from
BASIC by typing

PR*3

To act ivate the 80 -column firmware from the Monitor, type 3 and
press | contrul~| -p. Notice that this is the same procedure you
use to activate a card in expansion slot 3. Any auxiliary card
installed in the auxiliary slot takes precedence over a card

installed in expansion slot 3: see the section "Switching I/O
Memory" in Chapter 6 for details.

Even though you activated the 80-column firmware by typing pr#3,
you should never deactivate it by typing PR*o, because that just
disconnects the firmware, leaving several soft swi tches still set for
80-column operation. Instead, type the sequence | ESC j | control - ) -q
(see Table 3-6).

If there is no 80-column text card in your Apple lie, you can still

activate the 80-column firmware and use it with a 40-column

display. First, set the INTC3R0M soft-switch located at

$C00A (491 62); this switch is described in Chapter 6 in the section

"Switching I/O Memory". Then type PR*3 to transfer control to the

firmware.

When the 80-column firmware is active without a card in the
auxiliary slot, it does not work quite the same as it does with a
card. The functions that clear the display (CLREOL, cleolz,
clreop, and HOME) work as if the firmware were inactive: they
always clear to black, even in inverse format. Also, interrupts are
locked out throughout long operations such as clearing the
display. With a card installed, the firmware enables interrupts
periodically during these long operations.

Warning

If you do not have either an 80-column text card in the auxiliary slot
or a terminal card of some kind in expansion slot 3, don't try to
activate the firmware by simply typing PR*3. Typing PR#3 with no card
installed transfers control to the empty connector, with unpredictable
results.

Programs activate the 80-column firmware by transferring control
to address $C300. If there is no card in the auxiliary slot, you must
set the INTC3R0M soft switch first . To deactiv ate the 80-column
firmware from a program, write a [ control] -u character via
subroutine COUT.

46 Built-in I/O Firmware

The Old Monitor

The older model Apple lis and Apple II Pluses included a different
version of the System Monitor. It had the same standard I/O
subroutines, but a few of their features were different; for
example, there were no arrow keys for cursor motion. When you
start the Apple lie with a DOS or BASIC disk and it loads Integer
BASIC into the bank-switched area in RAM, it loads the old
Monitor (sometimes called the Autostart Monitor) along with it.
When you type INT from Applesoft to activate Integer BASIC, you
also activate this copy of the old Monitor, which remains active
until you either type FP to switch back to Applesoft, which uses
the new Monitor in ROM, or type

PR#3

to activate the 80-column firmware. Part of the firmware's
initialization procedure checks to see which version of the
Monitor is in RAM. If it finds the old Monitor, it replaces it with a
copy of the new Monitor from ROM. After the firmware has
copied the new Monitor into RAM, it remains there until the next
time you start up the system.

The Standard I/O Links

When you call one of the character I/O subroutines (COUT and
RDKEY), the first thing that happens is an indirect jump to an
address stored in programmable memory. Memory locations used
for transferring control to other subroutines are sometimes called
vectors; in this manual, the locations used for transferring control
to the I/O subroutines are called the I/O links. In a Apple lie
running without a Disk Operating System, each I/O link is
normally the address of the body of the subroutine (C0UT1 or
key IN). If a Disk Operating System (DOS) is running, one or both
of these links hold the addresses of the corresponding DOS I/O
routines instead. (DOS maintains its own links to the standard
I/O subroutines.)

By calling the I/O subroutines that jump to the link addresses
instead of calling the standard subroutines directly, you ensure
that your program will work properly in conjunction with other
software, such as DOS or a printer driver, that changes one or
both of the I/O links. For the purposes of this chapter, we shall
assume that the I/O links contain the addresses of the standard
I/O subroutines C0UT1 and key IN. For more information about the
I/O links, see the section "Changing the Standard I/O Links" in
Chapter 6.

Using the I/O Subroutines 47

Standard Output Features

The standard output routine is named COUT, pronounced C-out,
which stands for character out. CDUT normally calls CQUT1 , which
sends one character to the display, advances the cursor position,
and scrolls the display when necessary. C0UT1 restricts its use of
the display to an active area called the text window, described
below.

COUT Output Subroutine

Your program makes a subroutine call to $fded with a character
in the accumulator. COUT then passes control via the output link
csw to the current output, normally cduti, which takes the
character in the accumulator and writes it out. If the accumulator

Table 3.3a Control Characters with
CDUT1.

(1) Only available when 80-column
firmware is active.

(2) Only works from the keyboard.

(3) Doesn't work from the keyboard.

Control ASCII Apple lie Action

Character Name Name Taken by CQUT1

Notes

CONTROL

[ CONTROL

CONTROL

- G (BEL) bell

- H (BS) backspace

- J (LF) line feed

- K (VT) clear EOS

- L (FF) clear

- M (CR) return

- N (SO) normal

- D (SI) inverse

- Q (DC1) 40-column

- R (DC2) 80-column
S (DS3) stop-list

Produces a 1000 Hz tone for
0.1 second.

Moves cursor position one
space to the left; from left edge
of window, moves to right end
of line above.

Moves cursor position down to
next line in window; scrolls if
needed.

Clears from cursor position to
the end of the window.

Moves cursor position to
upper-left corner of window and
clears window.

Moves cursor position to left
end of next line in window;
scrolls if needed.

Sets display format normal.

Sets display format inverse.

Sets display to 40-column.

Sets display to 80-column. 1

1,3
1,3

Stops sending characters to the 1,2
display, until a key is pressed.

Built-in I/O Firmware

contains an uppercase or lowercase letter, a number, or a
special character, the accumulator contains a control character,
CDUT1 either performs one of the special functions described
below or ignores the character.

Each time you send a character to C0UT1 , it displays the character
at the current cursor position, replacing whatever was there, and
then advances the cursor position one space to the right. If the
cursor position is already at the right-hand edge of the window,
C0UT1 moves it to the left-most position on the next line down. If
this would move the cursor position past the end of the last line
in the window, C0UT1 scrolls the display up one line and sets the
cursor position at the left end of the new bottom line.

Table 3-3b Control Characters with
C0UT1 , continued

Control
Character

ASCII
Name

Apple lie
Name

Action Taken by C0UT1

Notes

(1 ) Only available when 80-column

- U

- V

- W

- Y

- Z

- \

(NAK)

(SYN)

(ETB)

(EM)

(SUB)
(FS)

quit

scroll

scroll-up

home

clear line
fwd. space

Deactivates 80-column
firmware, homes cursor,
and clears screen.

Scrolls the display down
one line, leaving the cursor
in the current position.

Scrolls the display up one
line, leaving the cursor in
the current position.

Moves cursor position to
upper-left corner of window
(but doesn't clear).

Clears the line the cursor
position is on.

Moves cursor position one

firmware is active.
(2) gotoXY is not supported under
BASIC: see the Apple Pascal
Operating System Reference Manual.

| CONTROL |

| CONTROL |
| CONTROL |

1
1

CONTROL

(GS) clear EOL

(RS) gotoXY

space to the right; from
right edge of window,
moves it to left end of line
below.

Clears line from cursor 1

position to the right edge of
the window.

Using the next two
characters, minus 32, as
one-byte X and Y values,
moves the cursor position
toCH=X, CV=Y.

1, 2

Standard Output Features

The cursor position is controlled by the values in memory
locations 36 and 37 (hexadecimal *24 and $25). These locations
are named CH, for cursor horizontal, and cv, for cursor vertical.
C0UT1 does not display a cursor, but the input routines described
below do, and they use this cursor position. If some other routine
displays a cursor, it will not necessarily put it in the cursor
position used by C0UT1 .

Control Characters with CDUT1

C0UT1 does not display control characters. Instead, the control
characters listed in Tables 3-3a and 3-3b are used to initiate
some action by the firmware. Other control characters are
ignored. Most of the functions listed here can also be invoked
from the keyboard, either by typing the control character listed or
by using the appropriate escape code, as described in the
section "Escape Codes with KEY IN". The stop-list function,
described separately, can only be invoked from the keyboard.

The Stop-list Feature

When you are using any program that displays text via CDUT1 , you
can make it stop updating the display by holding down the
| control I key and pressing the s key. Whenever coun gets a
carriage return from the program, it checks to see if you have
typed a fcONTROL \ - s . If you have, C0UT1 stops and waits for you to
press another key. When you want coun to resume, press
another key; coun will send the carriage return it got earlier to
the display, then continue normally. The character code of the
key you pressed to resume displaying is ignored unless it is a
r control | -c. C0UT1 passes I control I -c back to the program; if
it is a BASIC program, this enables you to terminate the program
while in stop-list mode.

The Text Window

After starting up the computer or after a reset, C0UT1 uses the
entire display. However, you can restrict C0UT1 's activity to any
rectangular portion of the display you wish. The active portion of
the display is called the text window. couTi puts characters only
into the window; when it reaches the end of the last line in the
window, it scrolls only the contents of the window.

50 Built-in I/O Firmware

You can set the top, bottom, left side, and width of the text
window by storing the appropriate values into four locations in
memory. This enables your programs to control the placement of
text in the display and to protect other portions of the screen
from being written over by new text.

Memory location 32 (hexadecimal $20) contains the number of the
leftmost column in the text window. This number is normally 0,
the number of the leftmost column in the display. In a 40-column
display, the maximum value for this number is 39 (hexadecimal
$27); in an 80-column display, the maximum value is 79
(hexadecimal $4F).

Memory location 33 (hexadecimal $21 ) holds the width of the text
window. For a 40-column display, it is normally 40 (hexadecimal
$28); for an 80-column display, it is normally 80 (hexadecimal
$50). C0UT1 truncates the width to an even value.

Warning

Be careful not to let the sum of the window width and the leftmost
position in the window exceed the width of the display you are using
(40 or 80). If this happens, it is possible for coun to put characters
into memory locations outside the display page, possibly destroying
programs or data.

Memory location 34 (hexadecimal *22) contains the number of the
top line of the text window. This is normally 0, the topmost line in
the display. Its maximum value is 23 (hexadecimal $17).

Memory location 35 (hexadecimal *23) contains the number of the
bottom line of the screen, plus 1. It is normally 24 (hexadecimal
$18) for the bottom line of the display. Its minimum value is 1.

Warning

Any time you change the boundaries of the text window, you should
make sure that the current cursor position (stored at CH and cv) is
inside the new window. If it is outside, it is possible for COUTito put
characters into memory locations outside the display page, possibly
destroying programs or data.

Standard Output Features

Table 3-4 Text Window Memory
Locations

Window
Parameter

Location
Dec Hex

Minimum

Value:
Dec Hex

Normal Values:

40col. 80col.

Dec Hex Dec Hex

Maximum
40col.
Dec Hex

Values:

80col.
Dec Hex

Left Edge

$20

$27

79 $4F

Width

$21

$28

$50

$28

80 $50

Top Edge

$22

$17

23 $17

Bottom Edge

$23

$18

24 $18

Table 3-4 summarizes the memory locations and the possible
values for the window parameters.

Inverse and Flashing Text

Subroutine CDUT1 can display text in normal format, inverse
format, or, with some restrictions, flashing format. The display
format for any character in the display depends on two things:
the character set being used at the moment, and the setting of
the two high-order bits of the character's byte in the display
memory.

As it sends your text characters to the display, C0UT1 sets the
high-order bits according to the value stored at memory location
50 (hexadecimal $32). If that value is 255 (hexadecimal $FF),
C0UT1 sets the characters to display in normal format; if the value
is 63 (hexadecimal $3F), C0UT1 sets the characters to inverse
format. If the value is 127 (hexadecimal $7F) and if you have
selected the primary character set, the characters will be
displayed in flashing format. Note that flashing format is not
available in the alternate character set.

To control the display format of the characters, routine C0UT1 uses
the value at location 50 as a logical mask to force the setting of
the two high-order bits of each character byte it puts into the
display page. It does this by performing the logical AND function
on the data byte and the mask byte. The result byte contains a
in any bit that was in the mask. The version of C0UT1 in the 80-
column firmware changes only the high-order bit of the data.

Built-in I/O Firmware

Table 3-5 Text Format Control Values

Note: These mask values apply only to
the primary character set (see text).

Mask value
Dec Hex

Display format

255

$FF

Normal, uppercase and lowercase

127

$7F

Flashing, uppercase and symbols

$3F

Inverse, uppercase and lowercase

If the 80-column firmware is inactive and you store a mask value at
location 50 with zeros in its low-order bits, C0UT1 will mask out those
bits in your text. As a result, some characters will be transformed
into other characters. You should set the mask only to the values
given in Table 3-5.

If you set the mask value at location 50 to 127 (hexadecimal
$7F), the high-order bit of each result byte will be 0, and the
characters will be displayed either as lowercase or as flashing,
depending on which character set you have selected. Refer to
the tables of display character sets in Chapter 2. In the primary
character set, the next-highest bit, bit 6, selects flashing format
with uppercase characters. With the primary character set you
can display lowercase characters in normal format and uppercase
characters in normal, inverse, and flashing formats. In the
alternate character set, bit 6 selects lowercase or special
characters. With the alternate character set you can display
uppercase and lowercase characters in normal and inverse
formats. Switching between character sets is described in the
section "Display Mode Switching" in Chapter 2.

Standard Input Features

The Apple lie's firmware includes two different subroutines for
reading from the keyboard. One subroutine is named RDKEY, which
stands for read key. It calls the standard character input
subroutine key IN, which accepts one character at a time from the
keyboard. The other subroutine is named GETJJ^ which stands for
get line. By making repeated calls to RDKEY, GETLN accepts a
sequence of characters terminated with a carriage return, getln
also provides on-screen editing features: see the section "Editing
with GETLN".

Standard Input Features

RDKEY Input Subroutine

A program gets a character from the keyboard by making a
subroutine call to rdkey at memory location $fdoc. rdkey sets the
character at the cursor position to flash, then passes control via
the input link ksw to the current input subroutine, which is
normally KEY IN.

RDKEY displays a cursor at the current cursor position, which is
immediately to the right of whatever character you last sent to
the display (normally by using the COUT routine, described above).
The cursor displayed by RDKEY is a flashing version of whatever
character happens to be at that position on the screen. It is
usually a space, so the cursor appears as a blinking rectangle.

The method rdkey uses to display a cursor works as it did on the
older model Apple lis, which don't display lowercase characters.
If you are running an Integer BASIC program with the 80-column
firmware inactive, the RDKEY-style cursor is still appropriate. With
lowercase characters or with the alternate character set, this
method of displaying a cursor is no longer satisfactory.

KE Y I N Input Subroutine

key IN is the standard input subroutine. When called, it waits until
the user presses a key, then returns with the key code in the
accumulator.

The problem of displaying a cursor without using flashing format
is handled by keyin. If the 80-column firmware is inactive, keyin
displays a cursor by alternately storing a checkerboard block in
the cursor location, then storing the original character, then the
checkerboard again. If the firmware is active, keyin displays a
steady inverse space (rectangle), unless you are in escape
mode, when it displays a plus sign (+) in inverse format.
(Escape mode is described in the next section.)

KEYIN also generates a random number. While it is waiting for the
user to press a key, KEYIN repeatedly increments the 16-bit
number in memory locations 78 and 79 (hexadecimal *4E and *4F).
This number keeps increasing from to 65535, then starts over
again at 0. The value of this number changes so rapidly that
there is no way to predict what it will be after a key is pressed. A
program that- reads from the keyboard can use this value as a
random number or as a seed for a pseudo-random number
routine.

54 Built-in I/O Firmware

When the user presses a key, key in accepts the character, stops
displaying the cursor, and returns to the calling program with the
character in the accumulator.

Escape Codes with key IN

key IN has many special functions that you invoke by typing
escape code s on th e keyboard. An escape code is obtained by

Table 3-6 Escape Codes

(1) Old-style cursor-control key: see
text.

(2) Cursor-control key: see text.

(3) This code functions only when the
80-column firmware is active.

Escape Code

Function

Notes

Clears the window and homes the cursor

Moves the cursor up one line

Moves the cursor right one space

Moves the cursor left one space

Moves the cursor down one line

Clears to the end of the line

Clears to the bottom of the window

Moves the cursor up one line and turns on
escape mode

Moves the cursor left one space and turns on
escape mode

Moves the cursor right one space and turns on
escape mode

Moves the cursor down one line and turns on
escape mode

Turns on restricted-case mode

Turns off restricted-case mode

Switches to 40-column mode, homes the
cursor, and clears the screen

Switches to 80-column mode, homes the
cursor, and clears the screen

Deactivates the 80-column firmware

| ESC |@

| ESC | A

| ESC | B

| ESC | C

| ESC | D

| ESC | E

| ESC | F

| ESC | I

| ESC | |

ESC | J

| ESC [*-

| ESC | K

| ESC |-*~

| ESC | M

1 Esc 1 \

[ESC J R

| ESC | T

| ESC | 4

| ESC | 8

| ESC | [ CONTRO

L|-Q

Standard Input Features

Table 3-6 inclu des th ree sets of cursor-control keys. The first set
consists of the 1 ESC | key followed by a, B, c, or D. The letter keys
can be either uppercase or lowercase. These keys are the
standard cursor-motion keys on older Apple II models; they are
present on the Apple Me primarily for compatability with programs
written for old machines.

Cursor Motion in Escape Mode

The second and third set of cursor-control keys are listed
together because they activate escape mode. In escape mode,
you ca n keep using the cursor-motion keys without pressing the
1 ESC 1 key again. This enables you to perform repeated cursor
moves by holding down the appropriate key.

When the 80-column firmware is active, you can tell when KEY IN
is in escape mode: it displays a plus sign in inverse format as
the cursor. You leave escape mode by typing any key other than
a cursor-motion key.

The escape codes with the directional arrow keys are the
standard cursor-motion keys on the Apple Me. The escape codes
with the I, J, K, and m keys are the standard cursor-motion keys
on the Apple II Plus, and are present on the Apple Me for
compatability with the Apple II Plus. On the Apple Me, the escape
codes with the I, J, K, and M keys function with either uppercase
or lowercase letters.

G E T L N Input Subroutine

Programs often need strings of characters as input. While it is
possible to call rdkey repeatedly to get several characters from
the keyboard, there is a more powerful subroutine you can use.
This routine is named GETLN, which stands for get line, and it
starts at location *FD6A. Using repeated calls to rdkey, GETLN
accepts characters from the standard input subroutine — usually
key in — and puts them into the input buffer located in the
memory page from *200 to *2FF. getln also provides the user with
on-screen editing and control features, described below in the
section "Editing with GETLN".

The first thing getln does when you call it is display a prompting
character, called simply a prompt. The prompt indicates to the
user that the program is waiting for input. Different programs use
different prompt characters, helping to remind the user which
program is requesting the input. For example, an input statement
in a BASIC program displays a question mark (?) as a prompt.

56 Built-in I/O Firmware

Table 3-7 Prompt Characters
*Note: Mini-assembler is available only
with Integer BASIC active.

The prompt characters used by the different programs on the
Apple Me are shown in Table 3-7.

getln uses the character stored at memory location (hexadecimal
*33) as the prompt character. In an assembly-language program,
you can change the prompt to any character you wish. In BASIC,
changing the prompt character has no effect, because both
BASIC interpreters and the Monitor restore it each time they
request input from the user.

Prompt
Character

Program Requesting Input

User's BASIC program (INPUT statement)

Integer BASIC

]

Applesoft BASIC

Firmware Monitor

Mini-assembler*

As the user types the character string, getln sends each
character to the standard output routine — normally cduti —
which displays it at the previous cursor position and puts the
cursor at the next available position on the display, usually
immediately to the right. As the cursor travels across the display,
it indicates the position where the next character will be
displayed.

GETLN stores the characters in its buffer, starting at memory
location *200 and using the X register to index the buffer. GETLN
cont inues to a ccept and display characters until the user presses
the I RETURN ] key; then it clears the remainder of the line the
cursor is on, stores the carriage-return code in the buffer, sends
the carriage-return code to the display, and returns to the calling
program.

The maximum line-length that GETLN can handle is 255 characters.
If the user types more than this, getln sends a backslash (\)and
a carriage return to the display, cancels the line it has accepted
so far, and starts over. To warn the user that the line is getting
full, getln sounds a bell (tone) at every keypress after the 248th.

Standard Input Features

In the Apple II and the Apple II Plus, the getln routine converts all
inputs to uppercase, getln in the Apple lie does not do this, even in
Apple II mode. To get uppercase input for BASIC, use the

caps lock key or switch to restricted-case mode using the escape
sequence shown in Table 3-6. With restricted-case active, letters are
automatically shifted to uppercase except inside quotation marks.

Editing with GETLN

Subroutine getln provides the standard on-screen editing features
used by the BASIC interpreters and the Monitor. For an
introduction to editing with these features, refer to the Applesoft
Tutorial. Any program that uses getln for reading the keyboard
has these features.

Cancel Line

Any time you are typing a line, pressing | CONTROL | -x causes
getln to cancel the line. GETLN displays a backslash (/ ) and
issues a carriage return, then displays the prompt and waits for
you to type a new line, getln takes the same action when you
type more than 255 characters, as described above.

Backspace

When you press the I LEFT-ARROW | key, getln moves its buffer
pointer back one space, effectively deleting the last character in
its buffer. It also sends a backspace character to routine cout,
which moves the display position and the cursor back one space.
If you type another character now, it will replace the character
you backspaced over, b oth on the displ ay and in the line buffer.
Each time you press the | LEFT-ARROW [ key, it moves the cursor left
and deletes another character until you reach the beginning of
the line. If you then press the I LEFT -arrow"] key one more time,
you have effectively cancelled the line, and GETLN issues a
carriage return and displays the prompt.

Retype

The 1 right-ARROM | key has a function that is complementa ry to
the backspace function. When you press the | RIGHT- ARROW ] key,
getln picks up the character at the display position just as if it
had been typed on the keyboard. You can use this procedure to
pick up characters that you have just deleted by backspacing
across them. You can use the backspace and retype functions
with the cursor-motion functions to edit data on the display (see
the earlier section "Cursor Motion in Escape Mode").

58 Built-in I/O Firmware

r ■—

Chapter 4

Memory Organization

61 Main Memory Map

63 RAM Memory Allocation

63 Reserved Memory Pages

64 Page Zero

64 The 6502 Stack

64 The Input Buffer

65 Link-address Storage
65 The Display Buffers

68 Bank-switched Memory

69 Setting Bank Switches

71 Auxiliary Memory and Firmware
73 Memory Mode Switching

76 Auxiliary-memory Subroutines

77 Moving Data to Auxiliary Memory

78 Transferring Control to Auxiliary Memory

79 The Reset Routine

80 The Cold-start Procedure

80 The Warm-start Procedure

81 Forced Cold Start
81 The Reset Vector
83 Automatic Self-test

Memory Organization

ii — J

Chapter 4

Memory Organization

The Apple lie's 6502 microprocessor can address 65,536 (64K)
memory locations (K stands for 1024; refer to the glossary). All of
the Apple lie's programmable storage (RAM, for random-access
memory), read-only storage (ROM, for read-only memory) and
input and output devices are allocated locations in this 64K
address space. Some functions share the same addresses — but
not at the same time. For information about these shared
address spaces, see the section "Bank-switched Memory" in this
chapter and the sections "Other Uses of I/O Memory Space"
and "Expansion ROM Space" in Chapter 6.

All input and output in the Apple lie is memory mapped. In this
chapter, the I/O memory spaces are described simply as blocks
of memory. For details of the built-in I/O features, refer to the
descriptions in Chapters 2 and 3. For information about I/O
operations with peripheral cards, refer to Chapter 6.

People often refer to the Apple lie's memory in 256-byte blocks
called pages. One reason for this is that a one-byte address
counter or index register can specify one of 256 different
locations. Thus, page consists of memory locations from to
255 (hexadecimal *o to *ff), inclusive. Page 1 consists of
locations 256 to 51 1 (hexadecimal *1 00 to *1 FF — note that the
page number is the high-order part of the hexadecimal address).
Don't confuse this kind of page with the display buffers in the
Apple Me, which are sometimes referred to as Page 1 and
Page 2.

Main Memory Map

The map of the main memory address space in Figure 4-1
shows the functions of the major areas of memory. For more
details on the I/O space from 48K to 52K (*C000 through $CFFF),

Main Memory Map 61

refer to Chapter 2 and Chapter 6; the bank-switched memory in
the memory space from 52K to 64K ($dooo through $ffff) is
described below.

Figure 4-1 System Memory Map

FFFF

D000

ROM

BANK-
SWITCHED
RAM

CFFF

COOO

I/O

BFFF

8000

MAIN
RAM

7FFF

4000

3FFF

0000

Memory Organization

Figure 4-2 RAM Allocation Map

BFFF
8000

7FFF

6000

5FFF
4000

Page 2

High-resolution
graphics
display buffers

Text and low-resolution
graphics display buffers

Reserved pages

RAM Memory Allocation

As Figure 4-1 shows, the major portion of the Apple lie's memory
space is allocated to programmable storage (RAM). Figure 4-2
shows the areas allocated to RAM. The main RAM memory
extends from location to location 491 51 (hex $BFFF), and
occupies pages through 191 (hexadecimal $BF). There is also
RAM storage in the bank-switched space from 53248 to 65535
(hexadecimal $D000 to *FFFF), described in a separate section of
this chapter, and auxiliary RAM on the 80-column text card or the
extended 80-column text card, described in Chapter 6.

Reserved Memory Pages

Most of the Apple He's RAM is available for storing your
programs and data. However, a few RAM pages are reserved for
the use of the Monitor firmware and the BASIC interpreters. The
reserved pages are described below.

The system does not prevent your using these pages, but if you do
use them, you must be careful not to disturb the system data they
contain, or you will cause the system to malfunction.

RAM Memory Allocation

Page Zero

Several of the 6502 microprocessor's addressing modes require
the use of addresses in page zero, also called zero page. The
Monitor, the BASIC interpreters, and DOS all make extensive use
of page zero.

To use indirect addressing in your assembly-language programs,
you must store base addresses in page zero. At the same time,
you must avoid interfering with the other programs that use page
zero — the Monitor, the BASIC interpreters, and the Disk
Operating Systems. One way to avoid conflicts is to use only
those page-zero locations not already used by other programs.
Tables 4-1, 4-2, 4-3, and 4-4 show the locations in page zero
used by the Monitor, Applesoft BASIC, Integer BASIC, and
DOS 3.3.

As you can see from the tables, page zero is pretty well used
up, except for a few bytes here and there. It's hard to find more
than one or two bytes that aren't used by either BASIC or the
Monitor or DOS. Rather than trying to squeeze your data into an
unused corner, you may prefer a safer alternative: save the
contents of part of page zero, use that part, then restore the
previous contents before you pass control to another program.

The 6502 Stack

The 6502 microprocessor uses page 1 as the stack — the place
where subroutine return addresses are stored, in first-in, last-out
sequence. Many programs also use the stack for temporary
storage of the registers (via push and pull operations). You can
do the same, but you should use it sparingly. The stack pointer
is eight bits long, so the stack can hold only 256 bytes of
information at a time. When you store the 257th byte in the
stack, the stack pointer repeats itself, or wraps around, so that
the new byte replaces the first byte stored, which is now lost.
This writing over old data is called stack overflow, and when it
happens, the program continues to run normally until the lost
information is needed, whereupon the program terminates
catastrophically.

The Input Buffer

The getln input routine, which is used by the Monitor and the
BASIC interpreters, uses page 2 as its keyboard-input buffer.
The size of this buffer sets the maximum size of input strings.
(Note- Applesoft only uses the first 237 bytes, although it permits

64 Memory Organization

you to type all 256.) If you know that you won't be typing any
long input strings, you can store temporary data at the upper end
of page 2.

Link-Address Storage

The Monitor and DOS 3.3 both use the upper part of page 3 for
link addresses or vectors. Table 4-10 shows the part of page 3
the Monitor uses; refer to the DOS Manual to see how DOS
uses page 3.

BASIC programs sometimes need short machine-language
routines. These routines are usually stored in the lower part of
page 3.

The Display Buffers

The primary text and low-resolution-graphics display buffer
occupies memory pages 4 through 7 (locations 1 024 through 20 47,
hexadecimal $0400 through *07FF). This entire 1024-byte area is
called display Page 1 , and it is not usable for program and data
storage. There are 64 locations in this area that are not
displayed on the screen; these locations are reserved for use by
the peripheral cards (see Chapter 6).

Display Page 2, the alternate text and low-resolution-graphics
display buffer, occupies memory pages 8 through 1 1 (locations
2048 through 3071 , hexadecimal $0800 through $0BFF). Most
programs do not use Page 2 for displays, so they can use this
area for program or data storage.

The primary high-resolution-graphics display buffer, called high-
resolution Page 1 , occupies memory pages 32 through 63
(locations 8192 through 16383, hexadecimal $2000 through
*3FFF). If your program doesn't use high-resolution graphics, this
area is usable for programs or data.

High-resolution-graphics Page 2 occupies memory pages 64
through 95 (locations 1G384 through 24575, hexadecimal *4000
through *sfff). Most programs use this area for program or data
storage.

For more information about the display buffers, see Chapter 2.

■— ^

RAM Memory Allocation 65

Table 4-1 Monitor Zero-page Usage

High Nybble Low Nybble of Address

Of Address $0 *1 $2 $3 $4 $5 $6 $7 $8 *9 $A $B $C $D $E $F

$00
$10
$20
$30
$40
$50
$60
$70
$80
$90
$A0
$B0
$C0
$D0
$E0
$F0

Table 4-2 Applesoft Zero-page Usage

High Nybble Low Nybble of Address

of Address $0 $1 $2 $3 $4 $5 $6 $7 $8 $9 $A $B $C $D $E $F

$00
$10
$20
$30
$40
$50
$60
$70
$80
$90
$A0
$B0
$C0
$D0
$E0
$F0

Memory Organization

Table 4-3 Integer BASIC Zero-page
Usage

High Nybble Low Nybble of Address

of Address $0 $1 $2 $3 $4 $5 $6 $7 $8 $9 $A $B $C $D *E $F

$00
$10
$20
$30
$40
$50
$60
$70
$80
$90
$A0
$B0
$C0
$D0
$E0
$F0

Table 4-4 DOS 3.3 Zero-page Usage

High Nybble Low Nybble of Address

of Address $0 $1 $2 $3 $4 $5 $6 $7 $8 $9 $A $B $C $D $E $F

$00
$10
$20
$30
$40
$50
$60
$70
$80
$90
$A0
$B0
$C0
$D0
$E0
$F0

• • •

■ -

RAM Memory Allocation

Bank-switched Memory

The memory address space from 52K to 64K (hexadecimal *dooo
through $ffff) is doubly allocated: it is used for both ROM and
RAM. The 12K bytes of ROM (read-only memory) in this address
space contain the Monitor and the Applesoft BASIC interpreter.
Alternatively, there are 16K bytes of RAM in this space. The
RAM is normally used for storing either the Integer BASIC
interpreter or part of the Pascal Operating System (purchased
separately).

You may be wondering why this part of memory has such a split
personality. Some of the reasons are historical: the Apple lie is
able to run software written for the Apple II and Apple II Plus
because it uses this part of memory in the same way they do. It
is convenient to have the Applesoft interpreter in ROM, but the
Apple lie, like an Apple II with a language card, is also able to
use that address space for other things when Applesoft is not
needed.

You may also be wondering how 1 6K bytes of RAM is mapped
into only 12K bytes of address space. The usual answer is that
it's done with mirrors, and that isn't a bad analogy: the 4K-byte
address space from S2K to S6K (hexadecimal $dooo through $dfff)
is used twice.

Switching different blocks of memory into the same address
space is called bank switching. There are actually two examples
of bank-switching going on here: first, the entire address space
from 52K to 64K ($D000 through $FFFF) is switched between ROM
and RAM, and second, the address space from 52K to S6K ($D000
to $DFFF) is switched between two different blocks of RAM.

Figure 4-3 Bank-switched Memory Map

FFFF
E000

ROM

RAM

DFFF
D000

RAM

Memory Organization

Setting Bank Switches

You switch banks of memory in the same way you switch other
functions in the Apple lie: by using soft switches. These soft
switches do three things: select either RAM or ROM in this
memory space; enable or inhibit writing to the RAM (write-
protect); and select the first or second 4K-byte bank of RAM in
the address space $dooo to $dfff.

Warning

Do not use these switches without careful planning. Careless
switching between RAM and ROM is almost certain to have
catastrophic effects on your program.

Table 4-5 shows the addresses of the soft switches for enabling
all combinations of reading and writing in this memory space. All
of the hexadecimal values of the addresses are of the form $C08x.
Notice that several addresses perform the same function: this is
because the soft switches are activated by combinations of
address bits. For example, any address of the form $C08x with a
1 in the low-order bit enables the RAM for writing. Similarly, bit 3
of the address selects which 4K block of RAM to use for the
address space *dooo-$dfff; if bit 3 is 0, the first bank of RAM is
used, and if bit 3 is 1 , the second bank is used.

Table 4-5 Bank Select Switches

(1 ) This switch write-enables RAM
and read-enables ROM.

(2) Two successive reads to this
switch enables RAM both for reading
and writing.

Switch

Write

Read

4K RAM Bank:

Address

RAM

ROM

First Second

Notes

»C080

•

$C081

*C082

*C083

$C084

*C085

$C086

$C087

*C088

•

$C089

•

SC08A

•

$C08B

•

$C08C

•

*C08D

•

SC08E

•

*C08F

•

Bank-switched Memory

When RAM is not enabled for reading, the ROM in this address
space is enabled. Even when RAM is not enabled for reading, it
can still be written to if it is write-enabled.

When you turn power on or reset the Apple Me, it initializes the
bank switches for reading the ROM and writing the RAM, using
the second bank of RAM. Note that this is different from the
reset on the Apple II Plus, which didn't affect the bank-switched
memory (the language card). On the Apple Me, you can't use the
reset vector to return control to a program in bank-switched
memory, as you could on the Apple II Plus.

When you are using Integer BASIC on the Apple He, reset works
correctly, restarting BASIC with your program intact. This happens
because the reset vector transfers control to DOS, and DOS resets
the switches for the current version of BASIC.

Note that you can't read one RAM bank and write to the other; if
you select either RAM bank for reading, you get that one for writing
as well.

You can't read from ROM in part of the bank-switched memory and
read from RAM in the rest: specifically, you can't read the Monitor in
ROM while reading bank-switched RAM. If you want to use the
Monitor firmware with a program in bank-switched RAM, first copy
the Monitor from ROM (locations *F800 through sffcb) into lower
RAM and then into bank-switched RAM.

To see how to use these switches, look at the following section
of an assembly-language program:

LDA

$C083

; SELECT 2ND 4K BANK
READ/NRITE

LDA

$C083

; BY TWO CONSECUTIVE

LDA

*$D0

; SET UP. . .

STA

BEGIN

; ...NEW...

LDA

#$FF

; ...MAIN-MEMORY...

STA

END

; ...POINTERS...

JSR

RAMTST

; . . .FOR 12K BANK

LDA

SC08B

; SELECT 1ST 4K BANK

JSR

RAMTST

; USE ABOVE POINTERS

LDA

$C088

; SELECT 1ST BANK 4

READS

Memory Organization

A9 80

LDA

#$80

E6 10

INC

TSTNUM

20 B8

JSR

WPTSINIT

AD 80

LDA

$C080

; SELECT 2ND BANK &
WRITE PROTECT

E6 10

INC

TSTNUM

A9 01

LDA

#PAT12K

20 58

JSR

WPTSINIT

AD 8B

LDA

*C08B

; SELECT 1ST BANK *
READ/WRITE

AD 8B

LDA

$C08B

; BY TWO CONSECUTIVE READS

E6 0E

INC

RWMODE

; FLAG RAM IN READ/WRITE

E6 10

INC

TSTNUM

A9 08

LDA

#PAT4K

20 58

JSR

WPTSINIT

The LDA instruction, which performs a read operation to the
specified memory location, is used for setting the soft switches.
The unusual sequence of two consecutive LDA instructions
performs the two consecutive reads that write-enable this area of
RAM; in this case, the data that are read are not used.

Auxiliary Memory and Firmware

By installing an optional card in the auxiliary slot, you can add
more memory to the Apple Me. One such card is the 80-column
text card, which has 1 K bytes of additional RAM for expanding
the text display from 40 columns to 80 columns.

Another optional card, the extended 80-column text card, has
64K of additional RAM. A 1K-byte area of this memory serves
the same purpose as the memory on the 80-column text card:
expanding the text display to 80 columns. The other 63K bytes
can be used as auxiliary program and data storage. If you use
only 40-column displays, the entire 64K bytes is available for
programs and data.

Warning

Do not attempt to use the auxiliary memory from a BASIC program.
The BASIC interpreter uses several areas in main RAM, including
the stack and the zero page. If you switch to auxiliary memory in
these areas, the BASIC interpreter fails and you must reset the
system and start over.

Auxiliary Memory and Firmware

K^^

Figure 4-4 Memory map with Auxiliary

Memory

FFFF

MAIN

AUXILIARY

_ 1

BANK-

D000

ROM

SWITCHED
RAM

|||^^

CFFF

I/O

COOO

BFFF

|y^^

MAIN

8000

RAM

AUXILIARY
RAM

7FFF

fe^

6000

JL^

5FFF

4000

High-resolution
graphics display buffers

lu;^

3FFF

1 1 1
1 1

2000

fty^M

1FFF

Text and low-resolution J

graphics display buffers y I p

p^,^

0000

As you can see by studying the memory map in Figure 4-4, the
auxiliary memory is broken into two large sections and one small
one. The largest section is switched into the memory address
space from 51 2 to 491 51 ($200 through *bfff). This space includes
the display buffer pages: as described in Chapter 2, space in
auxiliary memory is used for one half of the 80-column text
display. You can switch to the auxiliary memory for this entire
memory space, or you can switch just the display pages: see the
section "Memory Mode Switching", below.

If the only reason you are using auxiliary memory is for the 80-
column display, note that you can store into the display page in
auxiliary memory by using the sostore and PAGE2 soft switches
described in the section "Display Mode Switching" in Chapter 2.

■u

Memory Organization

The other large section of auxiliary memory is switched into the
memory address space from 52K to 64K ($D000 through $ffff).
This memory space and the switches that control it are described
above in the section "Bank-switched Memory". If you use the
auxiliary RAM in this space, the soft switches have the same
effect on the auxiliary RAM that they do on the main RAM: the
bank switching is independent of the auxiliary-RAM switching.

Note that the soft switches for the bank-switched memory, described
in the previous section, do not change when you switch to auxiliary
RAM. In particular, if ROM is enabled in the bank-switched memory
space before you switch to auxiliary memory, the ROM will still be
enabled after you switch. Any time you switch the bank-switched
section of auxiliary memory in and out, you must also make sure
that the bank switches are set properly.

When you switch in the auxiliary RAM in the bank-switched
space, you also switch the first two pages, from o to 51 1 (*oooo
through $01 FF). This part of memory contains page zero, which is
used for important data and base addresses, and page one,
which is the 6502 stack. The stack and zero page are switched
this way so that system software running in the bank-switched
memory space can maintain its own stack and zero page while it
manipulates the 48K address space (from $020 to *BFFF) in either
main memory or auxiliary memory.

Memory Mode Switching

Switching the 48K section of memory is performed by two soft
switches: the switch named RAMRD selects main or auxiliary
memory for reading, and the one named ramwrt selects main or
auxiliary memory for writing. As shown in Table 4-6, each switch
has a pair of memory locations dedicated to it, one to select
main memory, and the other to select auxiliary memory. Enabling
the read and write functions independently makes it possible for
a program whose instructions are being fetched from one
memory space to store data into the other memory space.

Warning

Do not use these switches without careful planning. Careless
switching between main and auxiliary memories is almost certain to
have catastrophic effects on the operation of the Apple lie. For
example, if you switch to auxiliary memory with no auxiliary memory
card installed, the program that is running will stop and you will
have to reset the Apple lie and start over.

Auxiliary Memory and Firmware

Writing to the soft-switch at location *C003 turns RAMRD on and
enables auxiliary memory for reading; writing to location $C002
turns RAMRD off and enables main memory for reading. Writing to
the soft-switch at location *C005 turns RAMWRT on and enables the
auxiliary memory for writing; writing to location $C004 turns RAMWRT
off and enables main memory for writing. By setting these
switches independently, you can use any of the four
combinations of reading and writing in main or auxiliary memory.

Auxiliary memory corresponding to text Page 1 and high-
resolution graphics Page 1 can be used as part of the address
space from* 0200 to *BFFF by using RAMRD and RAMWRT as described
above. These areas in auxiliary RAM can also be controlled
separately by using the switches described in the section
"Display Mode Switching" in Chapter 2. Those switches are
named sostore, PAGE2, and hires.

As shown in Table 4-6, the 80 store switch functions as an
enabling switch: with it on, the PAGE2 switch selects main memory
or auxiliary memory. With the hires switch off, the memory space
switched by PAGE2 is the text display Page 1, from $0400 to *07FF;
with hires on, PAGE2 switches both text Page 1 and high-resolution
graphics Page 1, from $2000 to *3FFF.

If you are using both the auxiliary-RAM control switches and the
auxiliary-display-page control switches, the display-page control
switches take priority: if 80STGRE is off, RAMRD and RAMWRT work for
the entire memory space from $0200 to *bfff, but if
80STORE is on, RAMRD and RAMWRT have no effect on the display
page. Specifically, if 80 STORE is on and HIRES is off, PAGE 2 controls
text Page 1 regardless of the settings of RAMRD and RAMWRT.
Likewise, if 80 STORE and HIRES are both on, PAGE2 controls both text
Page 1 and high-resolution graphics Page 1 , again regardless of

RAMRD and RAMWRT.

A single soft switch named ALTZP (for alternate zero page)
switches the bank-switched memory and the associated stack
and zero page area between main and auxiliary memory. As
shown in Table 4-6, writing to location *C009 turns altzp on and
selects auxiliary-memory stack and zero page; writing to the soft
switch at location $C008 turns altzp off and selects main-memory
stack and zero page for both reading and writing. The section
"Auxiliary-memory Routines", below, describes firmware that you
can call to help you switch between main and auxiliary memory.

74 Memory Organization

When these switches are on, auxiliary
memory is being used; when they are
off, main memory is being used.

There are three more locations associated with the auxiliary-
memory switches. The high-order bits of the bytes you read at
these locations tell you the settings of the three soft switches
described above. The byte you read at location *C01 3 has its high
bit set to 1 if RAMRD is on (auxiliary memory is read-enabled), or
if RAMRD is off (the 48K block of main memory is read-enabled).
The byte location $C01 4 has its high bit set to 1 if RAMNRT is on
(auxiliary memory is write-enabled), or if RAMWRT is off (the 48K
block of main memory is write-enabled). The byte at location
$coie has its high bit set to 1 if altzp is on (the bank-switched
area, stack, and zero page in the auxiliary memory are selected),
or if altzp is off (these areas in main memory are selected).

■ li

Table 4-6 Auxiliary-memory Select
Switches

(1)When 80ST0REison, the PAGE2
switch selects main or auxiliary display
memory.

(2) When 80STQREis on, the HIRES
switch enables you to use the PAGE2
switch to switch between the
high-resolution Page-1 area in main
memory or auxiliary memory.

Name

Function

Hex

Location

Decimal

Notes

m m

RAMRD

Read auxiliary memory
Read main memory
Read RAMRD switch

*C003
*C002
SC013

49155
49154
49171

-16381
-16382
-16365

Write
Write
Read

RAMWRT

Write auxiliary memory
Write main memory
Read RAMWRT switch

*C005
*C004
*C014

49157
49156
49172

-16379
-16380
-16354

Write
Write
Read

80STQRE

On: access display page
Off: use RAMRD, RAMWRT
Read 80STORE switch

SC001
*C000
*C018

49153
49152
49176

-16383
-16384
-16360

Write
Write
Read

PAGE2

Page 2 on (Aux. memory)
Page 2 off (Main memory)
Read PAGE2 switch

*C055
$C054
*C01C

49237
49236
49180

-16299
-16300
-163S6

1
1
Read

HIRES

On: access hi-res pages
Off: use RAMRD, RAMWRT
Read HI RES switch

*C057
SC056
*C01D

49239
49238
49181

-16297
-16298
-16355

2
2
Read

ALTZP

Auxiliary stack & z. p.
Main stack & zero page
Read ALTZP switch

*C009
*C008
$C016

49161
49160
49174

-16373
-16374
-16352

Write
Write
Read

Auxiliary Memory and Firmware

In order to have enough memory locations for all of the soft
switches and remain compatible with the Apple II and Apple II Plus,
the soft switches listed in Table 4-6 share their memory locations
with the keyboard functions listed in Table 2-2. The operations —
read or write — shown in Table 4-6 for controlling the auxiliary
memory are just the ones that are not used for reading the
keyboard and clearing the strobe.

Auxiliary-memory Subroutines

If you want to write assembly-language programs that use
auxiliary memory but you don't want to manage the auxiliary
memory yourself, you can use the built-in auxiliary-memory
subroutines. These subroutines make it possible to use the
auxiliary memory without having to manipulate the soft switches
described in the previous section.

The subroutines described below make it easier to use auxiliary
memory, but they do not protect you from errors. You still have to
plan your use of auxiliary memory to avoid catastrophic effects on
your program.

You use these built-in subroutines the same way you use the I/O
subroutines described in Chapter 3: by making subroutine calls to
their starting locations. Those locations are shown in Table 4-7.

Table 4-7 Auxiliary-memory Routines Subroutine Location Description

Name

AUXMOVE $C31 1 Moves data blocks between main and auxiliary memory

XFER *C314 Transfers program control between main and auxiliary

memory

76 Memory Organization

Moving Data to Auxiliary Memory

In your assembly-language programs, you can use the built-in
subroutine named auxmove to copy blocks of data from main
memory to auxiliary memory or from auxiliary memory to main
memory. Before calling this routine, you must put the data
addresses into byte pairs in page zero and set the carry bit to
select the direction of the move — main to auxiliary or auxiliary
to main.

Warning

Don't try to use auxmove to copy data in page zero or page one (the
6502 stack) or in the bank-switched memory ($dooo-$ffff). auxmove
uses page zero all during the copy, so it can't handle moves in the
memory space switched by altzp.

The pairs of bytes you use for passing addresses to this
subroutine are called A1 , A2, and A4, and they are used for
parameter passing by several of the Apple lie's built-in routines.
The addresses of these byte pairs are shown in Table 4-8.

Table 4-8 Parameters for AUXMOVE

Routine

Name Location Parameter passed

Carry 1 = Move from main to auxiliary memory
= Move from auxiliary to main memory

A1 L $3C Source starting address, low-order byte

A1H $3D Source starting address, high-order byte

A2L $3E Source ending address, low-order byte

A2H $3F Source ending address, high-order byte

A4L $42 Destination starting address, low-order byte

A4H $43 Destination starting address, high-order byte

Auxiliary Memory and Firmware

Put the addresses of the first and last bytes of the block of
memory you want to copy into A1 and A2. Put the starting
address of the block of memory you want to copy the data to
into A4.

The auxmdve routine uses the carry bit to select the direction to
copy the data. To copy data from main memory to auxiliary
memory, set the carry bit; to copy data from auxiliary memory to
main memory, clear the carry bit.

When you make the subroutine call to auxmove, the subroutine
copies the block of data as specified by the A registers and the
carry bit. When it is finished, the accumulator and the X and Y
registers are just as they were when you called it.

Transferring Control to Auxiliary Memory

You can use the built-in routine named XFER to transfer control to
and from program segments in auxiliary memory. You must set
up three parameters before using XFER: the address of the routine
you are transferring to, the direction of the transfer (main to
auxiliary or auxiliary to main), and which page zero and stack
you want to use.

Table 4-9 Parameters for XFER Name or Parameter passed

Routine Location

Carry 1 = Transfer from main to auxiliary memory

= Transfer from auxiliary to main memory

Overflow 1 = Use page zero and stack in auxiliary memory
= Use page zero and stack in main memory

$ 3ED Program starting address, low-order byte

*3EE Program starting address, high-order byte

Put the transfer address into the two bytes at locations *3ED and
$3EE, with the low-order byte first, as usual. The direction of the
transfer is controlled by the carry bit: set the carry bit to transfer
to a program in auxiliary memory; clear the carry bit to transfer to
a program in main memory. Use the overflow bit to select which
page zero and stack you want to use: clear the overflow bit to
use the main memory; set the overflow bit to use the auxiliary
memory.

78 Memory Organization

After you have set up the parameters, pass control to the XFER
routine by a jump instruction, rather than a subroutine call. XFER
saves the accumulator and the transfer address on the current
stack, then sets up the soft switches for the parameters you have
selected and jumps to the new program.

Warning

It is the programmer's responsibility to save the current stack pointer
somewhere in the current memory space before using xfer and to
restore it after regaining control. Failure to do so will cause program
errors.

The Reset Routine

To put the Apple lie into a known state when it has just been
turned on or after a program has malfunctioned, there is a
procedure called the reset routine. The reset routine is built into
the Apple lie's firmware, and it is initiated any time you turn
power on o r press the | RESET | key while holding down the
1 caNTRaL~l key. The reset routine puts the Apple lie into its normal
operating mode and restarts the resident program.

When you initiate a reset, hardware in the Apple lie sets the
memory-controlling soft switches to normal: main board RAM and
ROM are enabled, and, if there is an 80-column text or extended
80-column text card in the auxiliary slot, expansion slot 3 is
allocated to the built-in 80-column firmware. Auxiliary RAM is
disabled and the bank-switched memory space is set up to read
from ROM and write to RAM, using the second bank at *D00 0.

The reset routine sets the display-controlling soft switches to
display 40-column text Page 1 using the primary character set,
then sets the window equal to the full 40-column display, puts
the cursor at the bottom of the screen and sets the display
format to normal.

The reset routine sets the keyboard and display as the standard
input and output devices by loading the standard I/O links (see
Chapter 6). It turns annunciators and 1 off and annunciators 2
and 3 on, clears the keyboard strobe, turns off any active
accessory-card ROM (see Chapter 6) and outputs a bell (tone).

The Apple Me has three types of reset: power-on reset, also
called cold-start reset; warm-start reset; and forced cold-start
reset. The procedure described above is the same for any type
of reset. What happens next depends on the reset vector. The
reset routine checks the reset vector to determine whether it is

The Reset Routine

valid or not, as described below in the section, "The Reset
Vector". If the reset was caused by turning the power on, the
vector will not be valid, and the reset routine will perform the
cold-start procedure. If the vector is valid, the routine will perform
the warm-start procedure.

The Cold-start Procedure

If the reset vector is not valid, either the Apple lie has just been
turned on or something has caused memory contents to be
changed. The reset routine clears the display and puts the string
"Apple ][" at the top of the display. It loads the reset vector and
the validity-check byte as described below, then starts checking
the expansion slots to see if there is a disk drive controller card
in one of them, starting with slot 7 and working down. If it finds a
controller card, it initiates the bootstrap (startup) routine that
resides in the controller card's firmware. The bootstrap then loads
the Disk Operating System from the disk in drive 1 . When DOS
has been loaded, it displays other messages on the screen. If
there is no disk in the d isk drive, th e drive mo tor just keeps
spinning until you press I CONTROL - ] -! RESEt~~[ . For more information
about DOS and the startup procedure, see the DOS Manual.

If the reset routine doesn't find a controller card, or if you press
[ control | - | RESET ~|again before the startup procedure has been
completed, the reset routine will continue without using the disk,
and pass control to the built-in Applesoft interpreter.

The Warm-start Procedure

Whenever you press | control] - | reset ] when the Apple lie has
already completed a cold-start reset, the reset vector is still valid
and it is not necessary to reinitialize the entire system. The reset
routine simply uses the vector to transfer control to the resident
program, which is normally the built-in Applesoft interpreter. If the
resident program is indeed Applesoft, your Applesoft program
and variables are still intact. If you are using DOS, it is the
resident program and it restarts either Applesoft or Integer
BA SIC, w hichever you were using when you pressed | control ] -
I RESET I.

A program in bank-switched RAM cannot use the reset vector to
regain control after a reset, because the reset routine enables ROM
in the bank-switched memory space. If you are using Integer
BASIC, which is in the bank-switched RAM, you are also using
DOS, and it is DOS that controls the reset vector and restarts
BASIC.

80 Memory Organization

Forced Cold Start

If a program has loaded the reset vector to p oint to the beginning
of the program, as described below, pressing | control 1 - | RESET

causes a warm-start reset that uses the vector to transfer control
to that program. If you want to stop such a program without
turning the powe r off and on , you can for ce a cold-start r eset by
holding down the | control 1 key and the 1 open-apple | key, then
pressing and releasing the(j?ESET] key.

When you want to stop a program unconditionally — for example, to
start up the Apple He with some other pr ogram — y o u should use
the forced cold-start reset, | control | - f0PEN-flPPL£| -[ reset"] , insteadof
turning the power off and on.

Whenever you press | control ] - | RESET |, firm ware in the Apple lie
always checks to see whether either ] apple ] key is down. If the
| SOLID-APPLE ] key is down, with or without the | OPEN-APPLE"] key,
the firmware pe rforms the self-test described below. If only the
| OPEN-APPLE | key is down, the firmware starts a forced cold-start
reset. First, it destroys the program or data in memory by writing
two bytes of arbitrary data into each page of main RAM. The two
bytes that get written over in page 3 are the ones that contain
the reset vector. The reset routine then performs a normal cold-
start reset.

The Reset Vector

When you reset the Apple lie, the reset routine transfers control
to the resident program by means of an address stored in
page 3 of main RAM. This address is called a vector because it
directs program control to a specified destination. There are
several other vector addresses stored in page 3, as shown in
Table 4-10, including the interrupt vectors described in Chapter 6,
and the DOS vectors described in the DOS Manual.

The cold-start reset routine stores the starting address of the
built-in Applesoft interpreter, low-order byte first, in the reset
vector address at locations 1 01 o and 1 01 1 (hexadecimal $3F2 and
*3F3). It then stores a validity-check byte, also called the power-
up byte, at location 1 012 (hexadecimal $3F4). The validity-check
byte is computed by performing an exclusive-OR of the second
byte of the vector with the constant 1 65 (hexadecimal $A5). Each
time you reset the Apple He, the reset routine uses this byte to
determine whether the reset vector is still valid.

The Reset Routine

Table 4-10 Page 3 Vectors

You can change the reset vector so that the reset routine will
transfer control to your program instead of to the Applesoft
interpreter. For this to work, you must also change the validity-
check byte to the exc lus ive-DR of the high-order byte of your new
reset vector with the constant 165 ($A5). If you fail to do this,
then the next time you reset the Apple lie, the reset routine will
determine that the reset vector is invalid and perform a cold-start
reset, eventually transferring control to the disk bootstrap routine
or to Applesoft.

Vector address
Decimal Hex

1008
1009

1010 «3F2

1011 *3F3

Vector function

$3F0 Address of the subroutine that handles BRK requests

*3F1 (normally *59, *FA).

fer-

Reset vector (see text).

1012

$3F4 Power-up byte (see text).

1013
1014
1015

$3F5
$3FG
$3F7

Jump instruction to the subroutine that handles Applesoft
"&" commands (normally *4C, *58, *FF).

1016
1017

1018

*3F8
*3F9
$3FA

J ump instruct ion to the subroutine that handles user
( | CONTROL | -Y) commands.

L—

1019
1020
1021

$3FB
$3FC
«3FD

Jump instruction to the subroutine that handles
non-maskable interrupts.

1022 *3FE Interrupt vector (address of the subroutine that handles

1023 *3FF interrupt requests).

Memory Organization

/ -I

..»

The reset routine has a subroutine that generates the validity-
check byte for the current reset vector. You can use this
subroutine by doing a subroutine call to location -1 169
(hexadecimal *FB6F). When your program finishes, it can return
the Apple He to normal operation by restoring the original reset
vector and again calling the subroutine to fix up the validity-check
byte.

Automatic Self-test

If you reset the Apple lie by holding down the | control | key and
the [ SOLlD-ftPPLE | key while pressing and releasing the I RESET |
key, the reset routine will start running the built-in self-test.
Successfully running this test assures you that the Apple Me is
operational.

Warning

The self-test routine tests the Apple lie's programmable memory by
writing and then reading it. All programs and data in programmable
memory when you run the self-test are destroyed.

The self-test takes several seconds to run. While it is running,
the display changes from black to white and back twice. If the
test finishes normally, the Apple lie displays an "OK" message
and waits for you to request a normal reset.

If the self-test detects something wrong, it displays an error
message and stops. If you have been running programs prior to
running the self-test, some soft-switches could be on, causing the
self-test to fail and display an error message. If this happens,
turn the power off for several seconds, then turn it back on and
run the self-test again. If it still fails, there is really something
wrong; to get it corrected, contact your Apple dealer for service.

The Reset Routine

Using The Monitor

M*l

87 Invoking the Monitor

88 Syntax of Monitor Commands

89 Monitor Memory Commands
89 Examining Memory Contents
89 Memory Dump

92 Changing Memory Contents

93 Changing One Byte

93 Changing Consecutive Locations

94 Moving Data in Memory

96 Comparing Data in Memory

97 Monitor Register Command

97 Examining and Changing Registers

98 Monitor Cassette Tape Commands

98 Saving Data on Tape

99 Reading Data from Tape

101 Miscellaneous Monitor Commands

101 Display Inverse and Normal

102 Back to BASIC

102 Redirecting Input and Output

103 Hexadecimal Arithmetic

1 04 Special Tricks with the Monitor
104 Multiple Command Lines
104 Filling Memory

106 Repeating Commands

106 Creating Your Own Commands

107 Machine-language Programs

107 Running a Program

108 Disassembled Programs
110 The Mini-Assembler

113 Mini-Assembler Instruction Formats
115 Summary of Monitor Commands

Using the Monitor

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Chapter 5

Using The Monitor

The System Monitor is a set of subroutines in the Apple Me
firmware. The Monitor provides a standard interface to the built-in
I/O devices described in Chapter 2. The I/O subroutines
described in Chapter 3 are part of the System Monitor.

The Disk Operating System and the BASIC interpreters use
these subroutines by direct calls to their starting locations, as
described for the I/O subroutines in Chapter 3; the starting
addresses for all of the standard subroutines are listed in
Appendix C. If you wish, you can call the standard subroutines
from your programs in the same fashion.

You can perform most of the Monitor functions directly from the
keyboard. This chapter tells you how to use the Monitor to

• look at one or more memory locations

• change the contents of any location

• write programs in machine language to be executed directly
by the Apple lie's microprocessor

• save blocks of data and programs onto cassette tape and
read them back in again

• move and compare blocks of memory

• invoke other programs from the Monitor

Invoking the Monitor

The System Monitor starts at memory location *FF69 (decimal
65385 or - 1 5 1 ). To invoke the Monitor, you make a CALL statement
to this location from the keyboard or from a BASIC program.
When the Monitor is running, its prompting character, an asterisk
(* ), appears on the left side of the display screen, followed by a
blinking cursor.

Invoking the Monitor

To use the Monitor, you type commands at the keyboard. When
you have finished using the Monitor, you return t o the BASIC
language you were previously u sing by pressing [ control] -
! reset], by typing [ CONTR OL] -c and pressing j R ETURN ), or
by typing 3D0G, which executes the resident program — usually
Applesoft — whose address is stored in a jump instruction at
location $3D0.

Syntax of Monitor Commands

To give a command t o the Mon itor, you type a line on the
keyboard, then press ] return | . The Monitor accepts the line using
the standard I/O subroutine GETLN described in Chapter 3. A
Monitor command can be up to 255 characters in length, ending
with a carriage return.

A Monitor command can include three kinds of information:
addresses, data values, and command characters. You type
addresses and data values in hexadecimal notation. Hexadecimal
notation uses the ten decimal digits (0-9) and the first six letters
(A-F) to represents the sixteen values from to 15. A pair of
hexadecimal digits represents values from to 255, corresponding
to a byte, and a group of four hexadecimal digits can represent
values from to 65,536, corresponding to a word. Any address
in the Apple lie can be represented by four hexadecimal digits.

When the command you type calls for an address, the Monitor
accepts any group of hexadecimal digits. If there are fewer than
four digits in the group, it adds leading zeros; if there are more
than four hexadecimal digits, the Monitor uses only the last four
digits. It follows a similar procedure when the command syntax
calls for two-digit data values.

Each command you type consists of one command character,
usually the first letter of the command name. The Monitor
recognizes 22 different command characters. Some of them are
punctuation marks, some are uppercase letters, and some are
control characters. Note: although the Monitor recognizes and
interprets them, control characters typed on an input line do not
appear on the screen. (See the "Summary of Monitor
Commands" at the end of the chapter.)

This chapter contains many examples of the use of Monitor
commands. In the examples, the commands and values you type
are shown in a normal typeface and the responses of the Monitor
are in a computer typeface. Of course, when you perform the

88 Using the Monitor

examples, all of the characters that appear on the display screen
will be in the same typeface. Some of the data values displayed
by your Apple Me may differ from the values printed in these
examples, because they are variables stored in programmable
memory.

Monitor Memory Commands

When you use the Monitor to examine and change the contents
of memory, it keeps track of the address of the last location
whose value you inquired about and the address of the location
that is next to have its value changed. These are called the last
opened location and the next changeable location.

Examining Memory Contents

When you type the address of a memory location and press
| RETURN ] , the Monitor responds with the address you typed, a
dash, a space, and the value stored at that location, like this:

•E000
E000- 20
•33

0033-AA

Each time the Monitor displays the value stored at a location, it
saves the address of that location as the last opened location
and as the next changeable location.

Memory Dump

When you type a period (.) followed by an address, and then
press | return | , the Monitor displays a memory dump: the data
values stored at all the memory locations from the one following
the last opened location to the location whose address you typed
following the period. The Monitor saves the last location
displayed as both the last opened location and the ne^t
changeable location. In these examples, the amount of data
displayed by the Monitor depends on how much larger than the
last opened location the address after the period is.

Monitor Memory Commands

,:. -

m — -

- -I

■■■■ J

*.2B ^

• 20
0020- 00

0021 - 28 00 18 OF OC 00 00
0028- A8 OG DO 07

•300

0300- 99
*.315

0301- B9 00 08 OA OA OA 99
0308- 00 08 C8 DO F4 A6 2B A9
0310- 09 85 27 AD CC 03

*.32A

*_»!—-<

0316-

0318-

0320-

0328-

A memory dump includes several different items of information.
The first line in the dump begins with the address of the location
following the last opened location; all other lines begin with
addresses that end alternately in zeros and eights, and there are
never more than eight data values displayed on a single line in a
memory dump.

When the Monitor performs a memory dump, it starts at the
location immediately following the last opened location and
displays that address and the data value stored there. It then
displays the values of successive locations up to and including
the location whose address you typed, but only up to eight
values on a line. When it reaches a location whose address is a
multiple of eight— that is, one that ends with an 8 or a — it

displays that address as the beginning of a new line, then

continues displaying more values. , ,

90 Using the Monitor

—J

After the Monitor has displayed the value at the location whose
address you specified in the command, it stops the memory
dump and sets that location as both the last opened location and
the next changeable location. If the address specified on the
input line is less than the address of the last opened location, the
Monitor displays only the address and value of the location
following the last opened location.

You can combine the two commands, opening a location and
dumping memory, by simply concatenating them: type the first
address, a period, and the second address. This combination of
two addresses separated by a period is called a memory range.

♦300.32F

0300-

99 B9 00 08 0A 0A 0A 99

0308-

00 08 C8 DO F4 A6 2B A9

0310-

09 85 27 AD CC 03 85 41

0318-

84 40 8A 4A 4A 4A 4A 09

0320-

CO 85 3F A9 5D 85 3E 20

0328-

43 03 20 46 03 AS 3D 4D

•30.40

0030-

0038-

0040-

•E015.E025

E015-

E018-

E020-

Pressing the | return] key by itself causes the Monitor to display
one line of a memory dump; that is, a memory dump from the
location following the last opened location to the next multiple-of-
eight boundary. The Monitor saves the address of the last
location displayed as the last opened location and the next
changeable location.

Monitor Memory Commands

*5
0005- 00

• \ RETURN 1

00 00

» | RETURN |

0008- 00 00 00 00 00 00 00 00

*32

. ...... ■ ■-.■ . ■'■■■■ ..■'■ ■ ■ ■ ■ ' ■'-' ■■ ■'.' I

0032- FF

» RETURN

00 C2 05 C2

« | RETURN 1

0038- 1B FD DO 03 3C 00 3F 00

;•. ,-'-':' : ^ y : \; ■■■

Changing Memory Contents

The previous section showed you how to display the values
stored in the Apple lie's memory; this section shows you how to
change those values. You can change any location in
RAM (programmable memory) and you can also change the soft
switches and output devices by changing the locations assigned
to them.

Warning

Use these commands carefully. If you change the zero-page
locations used by Applesoft and DOS, you may lose programs or
data stored in memory.

Using the Monitor

Changing One Byte

The previous commands keep track of the next changeable
location; these commands make use of it. In the next example,
you open location 0, then type a colon followed by a value.

0000- 00
»:5F

The contents of the next changeable location have just been
changed to the value you typed, as you can see by examining
that location:

*0
0000- 5F

You can also combine opening and changing into one operation
by typing an address followed by a colon and a value. In the
example, you type the address again to verify the change.

•302:42
•302

0302- 42

When you change the contents of a location, the value that was
contained in that location disappears, never to be seen again.
The new value will remain until you replace it with another value.

Changing Consecutive Locations

You don't have to type a separate command with an address,
a colon, a value, and | return | for each location you want to
change. You can change the the values of up to eighty-five

Monitor Memory Commands

consecutive locations at a time (or even more, if you omit leading
zeros from the values) by typing only the initial address and
colo n followed by all the values separated by spaces, and ending
with | RETURN | . The Monitor will duly store the consecutive values
in consecutive locations, starting at the location whose address
you typed. After it has processed the string of values, it takes the
location following the last changed location as the next change-
able location. Thus, you can continue changing consecutive
locations without typing an address on the next input line by
typing another colon and more values. In these examples, you
first change some locations, then examine them to verify the
changes.

• 300:69 01 20 ED FD 4C 3

•300

0300- 69

RETURN

01 20 ED FD 4C 00 03

•10:0 1 2 3

*:4 5 6 7

• 10.17

0010- 00 01 02 03 04 05 06 07

Moving Data in Memory

You can copy a block of data stored in a range of memory
locations from one area in memory to another by using the
Monitor's move command. To move a range of memory, you must
tell the Monitor both where the data is now situated in memory
— the source locations — and where you want the copy to go —
the destination locations. You give this information to the Monitor
by means of three addresses: the address of the first location in
the destination and the addresses of the first and last locations in
the source. You specify the starting and ending addresses of the
source range by separating them with a period. You separate the
destination address from the range addresses with a less-than

94 Using the Monitor

character (<), which you may think of as an arrow pointing in the
direction of the move. Finally, you tell the Monitor that this is a
move command by typing the letter M. The format of the complete
move command looks like this:

{destination} < {start} . {end} M

When you type the actual command, the words in curly braces
should be replaced by hexadecimal addresses, and the braces
and spaces should be omitted. Here are some examples of
memory moves. First, you examine the values stored in one
range of memory, then store several values in another range of
memory; the actual move commands end with the letter M:

—4

• O.F

0000- 5F 00 05 07 00 00 00 00
0008- 00 00 00 00 00 00 00 00

»300:A9 8D 20 ED FD A9 45 20 DA FD 4C 00 03
•300.30C

0300- A9 8D 20 ED FD A9 45 20
0308- DA FD 4C 00 03

•0O00.30CM
•O.C

0000- A9 8D 20 ED FD A9 45 20
0008- DA FD 4C 00 03

•310 8.AM

•310.312

0310- DA FD 4C

*2<7.9M

•O.C

oooo-

0008-

A9 8D 20 DA FD A9 45 20
DA FD 4C 00 03

Monitor Memory Commands

The Monitor moves a copy of the data stored in the source range
of locations to the destination locations. The values in the source
range are left undisturbed. The Monitor remembers the last
location in the source range as the last opened location, and the
first location in the source range as the next changeable location.
If the second address in the source range specification is less
than the first, then only one value (that of the first location in the
range) will be moved.

If the destination address of the move command is inside the
source range of addresses, then strange (and sometimes
wonderful) things happen: the locations between the beginning of
the source range and the destination address are treated as a
sub-range and the values in this sub-range are replicated
throughout the source range. See the section "Special Tricks with
the Monitor" for an interesting application of this feature.

Comparing Data in Memory

You can use the verify command to compare two ranges of
memory using the same format you use to move a range of
memory from one place to another. In fact, the verify command
can be used immediately after a MOVE to make sure that the move
was successful. The verify command, like the MOVE command,
needs a range and a destination. The syntax of the VERIFY
command is:

{destination} < {start} . {end} v

The Monitor compares the values in the source locations with the
values in the locations beginning at the destination address. If
any values don't match, the Monitor displays the address at
which the discrepancy was found and the two values that differ.
In the example, you store data values in the range of locations
from to *D, copy them to locations starting at $300 with the MOVE
command, and then compare them using the VERIFY command.
When you use the verify command after you change the value
at location 6 to *E4, it detects the change.

96 Using the Monitor

• 0:D7 F2 E9 F4 F4 E5 EE AO E2 F9 AO C3 C4 C5

»300<0.DM

*300<0.DV

*6:E4

*300<0.DV

0006-E4 CEE)

If the verify command finds a discrepancy, it displays the
address of the location in the source range whose value differs
from its counterpart in the destination range. If there is no
discrepancy, verify displays nothing. The verify command
leaves the values in both ranges unchanged. The last opened
location is the last location in the source range, and the next
changeable location is the first location in the source range, just
as in the MOVE command. If the ending address of the range is
less than the starting address, the values of only the first
locations in the ranges will be compared. Like the move command,
the verify command also does unusual things if the destination
address is within the source range; see the section "Special
Tricks with the Monitor".

Monitor Register Command

Even though the actual contents of the 6502's internal registers
are changing as you use the Monitor, you can examine the
values that the registers contained at the time the Monitor gained
control, either because you called it or because the program you
are debugging stopped at a break (BRK). You can also store
new register values that will be used when you execute a
program from the Monitor using the GO command, described
below.

Examining and Changing Registers

When you call the Monitor, it stores the contents of the 6502
registers in memory. The registers are stored in the order A, X,
Y, P (processor status register), and S stack pointer), starting at
location *45 (decimal 69). When you give the Monitor a GO
command, the Monitor loads the registers from these five
locations before it executes the first instruction in your program.

Monitor Register Commands

Typing I CONTROL | -E and pressing 1 RETURN 1 invokes the Monitor's
examine command, which displays the stored register values and
sets the location containing the contents of the A-register as the
next changeable location. After using the examine command, you
can change the values in these locations by typing a colon and
then typing the new values separated by spaces. In the following
example, you display the registers, change the first two, and then
display them again to verify the change.

' [CONTROL 1 -E

A=0A X=FF Y=D8 P=B0 S=F8

»:B0 02

CONTROL

-E

= B0

X = 02

Y =

P-

= B0

S =

= F8

Monitor Cassette Tape Commands

The Apple lie has two jacks for connecting an audio cassette
tape recorder. With a recorder connected, you can use the
Monitor commands described below to save the contents of a
range of memory onto a standard cassette and recall it again for
later use.

Saving Data on Tape

The Monitor's write command saves the contents of up to 65,536
memory locations on cassette tape. To save a range of memory
on tape, give the Monitor the starting and ending addresses of
the range, followed by the letter w (for WRITE), like this:

{start} . {end} w

Don't press [ RETURN | yet: first, put the tape recor der in reco rd
mode and let the tape run for a second, then press fRETURN 1 . The
Monitor will write a ten-second tone onto the tape and then write
the data. The tone acts as a leader: later, when the Monitor
reads the tape, the leader enables the Monitor to get in step with
the signal from the tape. When the Monitor is finished writing the
range you specified, it will sound a bell (beep) and display a
prompt. You should rewind the tape and label it with the memory
range that's on the tape and what it's supposed to be.

98 Using the Monitor

Here's a small example you can save and use later to try out the
read command. Remember that you must start the c assette
recorder in record mode before you press | RETURN | after typing
the write command.

• O.FF FF AD 30 CO 88 DO 04 C6 01 FO 08 CA
DO F6 A6 00 4C 02 00 60

•0.14

oooo-

0008-

0010-

•0.14W

It takes about 35 seconds total to save the values of 4,096
memory locations preceded by the ten-second leader onto tape.
This works out to an average data transfer rate of about 1,350
bits per second.

The write command writes one extra value on the tape after it
has written the values in the memory range. This extra value is
the checksum, which is the eight-bit partial sum of all values in
the range. When the Monitor reads the tape, it uses this value to
determine if the data has been written and read correctly (see
below).

Reading Data from Tape

Once you've saved a memory range onto tape with the Monitor's
WRITE command, you can read that memory range back into the
computer by using the Monitor's READ command. The data values
you've stored on the tape need not be read back into the same
memory range from whence they came; you can tell the Monitor
to put those values into any memory range in the computer's
memory, provided that it's the same size as the range you
saved. The format of the READ command is the same as that of
the WRITE command, except that the command letter is R:

{start} . {end} R

Monitor Cassette Tape Commands

Once again, after typing the command, don't press [ RETURN

Instead, start the tape recorder in play mode and wait a few
seconds. Although the write command puts a ten-second leader
tone on the beginning of the tape, the READ command needs only
three seconds of this leader to lock on to the signal from the
tape. You should let a few seconds of tape go by before you
press I RETURN 1 to allow the tape recorder's output to settle down
to a steady tone.

This example has two parts. First, you set a range of memory to
zero, verify the contents of memory, and then type the READ
command, but don't press I RETURN | .

• 0:0 00000000000000000000
•0.14

0000- 00 00 00 00 00 00 00 00
0008- 00 00 00 00 00 00 00 00
0010- 00 00 00 00 00

*0.14R

Now start t he cassett e running in play mode, wait a few seconds,
and press | RETURN | . After the Monitor sounds the bell (beep) and
displays the prompt, examine the range of memory to see that
the values from the tape were read correctly:

til -

• 0.14

oooo-

0008-

0010-

•

After the Monitor has read all the data values on the tape, it
reads the checksum value. It computes the checksum on the
data it read and compares it to the checksum from the tape. If
the two checksums differ, the Monitor sends a beep to the
speaker and displays "err". This warns you that there was a
problem reading the tape and that the values stored in memory
aren't the values that were recorded on the tape. If the two
checksums match, the Monitor will just send out a beep and
display a prompt.

100

Using the Monitor

Miscellaneous Monitor Commands

mme.

frame

Butsi-

These Monitor commands enable you to change the video
display format from normal to inverse and back, and to assign
input and output to peripherals in expansion slots.

Display Inverse and Normal

You can control the setting of the inverse-normal mask location
used by the COUT subroutine (described in Chapter 3) from the
Monitor so that all of the Monitor's output will be in inverse
format. The INVERSE command, I, sets the mask such that all
subsequent inputs and outputs are displayed in inverse format.
To switch the Monitor's output back to normal format, use the
NORMAL command, N.

*0.F

0000- 0A OB 0C 0D 0E OF DO 04
0008- C6 01 F0 08 CA DO F6 A6

•I
♦O.F

0000- 0A 0B 0C 0D 0E OF DO 04
0008- C6 01 F0 08 CA DO FG A6

■N

O.F

0000- 0A 0B 0C 0D 0E OF DO 04
0008- C6 01 F0 08 CA DO F6 A6

Miscellaneous Monitor Commands

101

Back to BASIC

Use the BASIC command, 1 contrdl| -B , to leave the Monitor and
enter the BASIC that was active when you entered the Monitor.
Normally, this is Applesoft BASIC, unless you deliberately
switched to Integer BASIC. Any program or variables that you
had previously in BASIC will be lost. If you want to re-enter
BASIC with your previous pr ogram and variables intact, use the
continue BASlCcommand, | control | - c . If you a r e using th e
Apple Disk Operating System (DOS), press [ CONTROL | - 1 RESET | or
type

3D0G

to return to the language you were using, with your program and
variables intact.

If you type the latter command, make sure that the third character
you type is a zero, not a letter O. The letter G is the Monitor's GO
command, described below in the section "Machine-language
Programs".

Redirecting Input and Output

The printer command, activated by a I CONTROL [ -P , diverts all
output normally destined for the screen to an interface card in a
specified exapnsion slot, from 1 to 7. There must be an interface
card in the specified slot, or you will lose control of the computer
and your program and variables may be lost. The format of the
command is

{slot number} | CONTROL | -P

A printer command to slot number will switch the stream of
output characters back to the Apple lie's video display.

Warning

Don't give the printer command with slot number to deactivate the
80-column firmware, even though you used this command to
activate it in slot 3. The command works, but it just disconnects the
firmware, leaving some of the soft-switches set for 80-column
display.

102 Using the Monitor

I
I

■ ,J

I
I

■ *

■ . ..

■ A

■H

■

In much the same way that the printer command switches the
output stream, the keyboard command substitutes the interface
card in a specified expansion slot for the Apple lie's normal input
device, the keyboard. The format for the keyboard command is:

{slot number} [ CONTROL | -K

A slot number of for the KEYBOARD command directs the Monitor
to accept input from the Apple lie's built-in keyboard.

The PR I nter and keyboard commands are the exact equivalents of
the BASIC commands PR* and IN#. For more information on the
way those commands work, refer to the section "The Standard I/O
Links" in Chapter 3.

Hexadecimal Arithmetic

The Monitor will also perform one-byte hexadecimal addition and
subtraction. Just type a line in one of these formats:

{value} + {value}
{value} - {value}

The Apple lie performs the arithmetic and displays the result, as
shown in these examples:

♦20+13
= 33
•4A-C
= 3E

•FF+4
-03
•3-4
= FF

Miscellaneous Monitor Commands

103

Special Tricks with the Monitor

This section describes some more complex ways of using the
Monitor commands.

Multiple Command Lines

You can put as many Monitor commands on a single line as you
like, as long as you separate them with spaces and the total
number of characters in the line is less than 254. Adjacent
single-letter commands such as L, s, I , and N need not be
separated by spaces.

You can freely intermix all of the commands except the store (: )
command. Since the Monitor takes all values following a colon
and places them in consecutive memory locations, the last value
in a STORE must be followed by a letter command before another
address is encountered. You can use the normal command as the
required letter command in such cases; it usually has no effect
and can be used anywhere.

In the following example, you display a range of memory, change
it, and display it again, all with one line of commands.

♦ 300.307

300:18

1 N

300.302

0300-
0300-
•

00
18

00
69

00
01

00 00

If the Monitor encounters a character in the input line that it does
not recognize as either a hexadecimal digit or a valid command
character, it executes all the commands on the input line up to
that character, then grinds to a halt with a noisy beep and
ignores the remainder of the input line.

Filling Memory

The move command can be used to replicate a pattern of values
throughout a range of memory. To do this, first store the pattern
in the first locations in the range:

• 300:11 22 33

104 Using the Monitor

Remember the number of values in the pattern: in this case, it is
3. Use the number to compute addresses for the move command,
like this:

{start+ number} < {start} . {end-number} M

This MOVE command will first replicate the pattern at the locations
immediately following the original pattern, then replicate that
pattern following itself, and so on until it fills the entire range.

• 303<300.32DM

•300.32F

0300-

0308-

0310-

0318-

0320-

0328-

You can do a similar trick with the verify command to check
whether a pattern repeats itself through memory. This is
especially useful to verify that a given range of memory locations
all contain the same value. In this example, -you first fill the
memory range from $300 to $320 with zeros and verify it, then
change one location and verify again, to see the VERIFY
command detect the discrepancy:

• 300:0

•30K300.31FM

•301<300.31FV

•304:02

•30K300.31FV

0303-00 C02)
0304-02 (00)

Special Tricks with the Monitor

105

■:■■ : ■' -' "■ ■

Repeating Commands

You can create a command line that repeats one or more
commands over and over. You do this by beginning the part of
the command line that you want to repeat with a letter command,
such as N, and ending it with the sequence 34 :n, where n is a
hexadecimal number that specifies the position in the line of the
command where you want to start repeating; for the first
character in the line, n=0. The value for n must be followed with
a space in order for the loop to work properly.

This trick takes advantage of the fact that the Monitor uses an
index register to step through the input buffer, starting at location
$200. Each time the Monitor executes a command, it stores the
value of the index at location $34; when that command is
finished, the Monitor reloads the index register with the value at
location $34. By making the last command change the value at
location $34, you change this index so that the Monitor picks up
the next command character from an earlier point in the buffer.

The only way to stop a loop like this is to press I CONTROL
| reset [ ; that is how this example ends.

»N 300 302 34:0

0300-

0302-

0300-

0302-

0300-

0302-

0300-

0302-

0300-

0302-

0300-

0302-

030

Creating your Own Commands

The user command, I control j -Y , forces the Monitor to jump to
memory location $3F8. You can put a JMP instruction there that
jumps to your own machine-language program. Your program
can then examine the Monitor's registers and pointers or the
input buffer itself to obtain its data. For example, here is a

106 Using the Monitor

program th at displays everything on the input line after the

1 CONTROL] -Y . The program starts at location $300; the command

line that starts with *3F8 stores a jump to $300 at location *3F8.

*300:A4 34 B9 00 02 20 ED FD C8 C9 8D DO F5 4C 69 FF
«3F8:4C 00 03

« | CONTROL I -Y THIS IS A TEST

THIS IS A TEST

Machine-Language Programs

The main reason to program in machine language is to get more
speed. A program in machine language can run much faster than
the same program written in high-level languages such as BASIC
or Pascal, but the machine-language version usually takes a lot
longer to write. There are other reasons to use machine
language: you might want your program to do something that
isn't included in your high-level language, or you might just enjoy
the challenge of using machine language to work directly on the
bits and bytes.

If you have never used machine language before, you'll need to
learn the 6502 instructions listed in Appendix A. To become
proficient at programming in machine language, you'll have to spend
some time at it, and study one of the books on 6502 programming
listed in the Bibliography.

You can get a hexadecimal dump of your program, move it
around in memory, or save it on tape and recall it again using
the commands described in the previous sections. The Monitor
commands in this section are intended specifically for you to use
in creating, writing, and debugging machine-language programs.

Running a Program

The Monitor command you use to start execution of your
machine-language program is the GO command. When you type
an address and the letter G, the Apple lie starts executing
machine language instructions starting at the specified location. If
you just type the G, execution starts at the last opened location.

Machine-language Programs

107

The Monitor treats this program as a subroutine: it should end
with an RTS (return from subroutine) instruction to transfer control
back to the Monitor.

The Monitor has some special features that make it easier for
you to write and debug machine-language programs, but before
you get into that, here is a small machine-language program that
you can run using only the simple Monitor commands already
described. The program in the example merely displays the
letters A through Z: you store it starting at location $300, examine
it to be sure you typed it correctly, then type 300G to start it
running.

*300:A9 C1 20 ED FD 18 69 1 C9 DB DO F6 60
•300.30C

0300- A9 C1 20 ED FD 18 69 01
0308- C9 DB DO F6 60

•300G

ABCDEFGH IJKLMNOPQRSTUVWXYZ

Since programs that translate assembly
language into machine language are
called assemblers, a program like the
Monitor's list command that translates
machine language into assembly
language is called a disassembler.

Disassembled Programs

Machine-language code in hexadecimal isn't the easiest thing in
the world to read and understand. To make this job a little
easier, machine-language programs are usually written in
assembly language and converted into machine-language code
by programs called assemblers.

The word mnemonic comes from the
same root as memory and refers to
short acronyms that are easier to
remember than the hexadecimal
operation codes themselves: for
example, for clear carry you write clc
instead of $18.

The Monitor's list command displays machine-language code in
assembly-language form. Instead of unformatted hexadecimal
gibberish, the LIST command displays each instruction on a
separate line, with a three-letter instruction name, or mnemonic,
and a formatted hexadecimal operand. The LIST command also
converts the relative addresses used in branch instructions to
absolute addresses.

108

Using the Monitor

■_Jiii

i
i
i
i
i

The Monitor list command has the format:

{location} L

The LIST command starts at the specified location and displays
as much memory as it takes to make up a screenfull (20 lines) of
instructions, as shown in the following example:

>300L

0300-

LDA

#$C1

0302-

ED FD

JSR

$FDED

0305-

CLC

0306-

ADC

*$01

0308-

CMP

#$DB

030A-

BNE

$0302

030C-

RTS

030D-

BRK

030E-

BRK

030F-

BRK

0310-

BRK

0311-

BRK

0312-

BRK

0313-

BRK

0314-

BRK

0315-

BRK

0316-

BRK

0317-

BRK

0318-

BRK

0319-

BRK

The first seven lines of this example are the assembly-language
form of the program you typed in the previous example. The rest
of the lines are brk instructions only if this part of memory has
zeros in it: other values will be disassembled as other
instructions.

The Monitor saves the address that you specify in the LIST
command, but not as the last opened location used by the other
commands. Instead, the Monitor saves this address as the
program counter, which it uses only to point to locations within
programs. Whenever the Monitor performs a L I ST command, it
sets the program counter to point to the location immediately
following the last location displayed on the screen, so that if you
type another LIST command it will display another screenfull of
instructions, starting where the previous display
left off.

5— «

Machine-language Programs

109

The Mini-assembler

Without an assembler, you have to write your machine language
program, take the hexadecimal values for the opcodes and
operands, and store them in memory using the commands
covered in the previous sections. That is exactly what you did
when you ran the previous examples.

The Integer BASIC interpreter includes an assembler called the
Apple Mini-assembler that enables you to type programs into the
Apple Me using the same assembly-language format that the LIST
command displays. It is called a mini-assembler because it
doesn't include symbolic labels, an important feature of all full-
sized assemblers like the Assembler/Editor in the DOS Tool Kit
(Apple product number A2D0029).

Before you can use the Mini-assembler, the Apple Me has to be
running Integer BASIC. When you start up the computer using
DOS or either BASIC, the Apple Me loads the Integer BASIC
interpreter from the file named INTBASIC into the bank-switched
RAM.

To run Integer BASIC after you have started up the computer
with DOS, type

INT

The Apple Me displays the Integer prompt character (>) and a
cursor.

If you have not activated the 80-column firmware since you started
up with DOS, the cursor now looks like a blinking rectangle: it is
actually a space character displayed in flashing format. This is
evidence that the old Monitor is operating (see Chapter 3). The old
Monitor is loaded into RAM along with Integer BASIC and the mini-
assembler; the next time you activate the 80-column firmware, it
copies the current version of the Monitor from ROM into RAM. Once
this has happened, the current Monitor is active even with Integer
BASIC, and the cursor is either a blinking checkerboard or a steady
rectangle.

Now enter the Monitor by typing

CALL -151

Using the Monitor

After you enter the Monitor from Integer BASIC, invoke the Mini-
assembler by typing:

F666G

I
I
I

■

This is just the GO command described above starting the
program stored at location $F666 — the mini assembler. You can
tell that the mini-assembler is running because it displays an
exclamation point (!) as its prompt character. While the mini-
assembler is running, you can execute any Monitor command by
preceding it with a dollar sign (*). Aside from that, the Mini-
assembler has an instruction set and syntax all its own.

The Mini-assembler saves one address, that of the program
counter. Before you start to type a program, you must set the
program counter to point to the location where you want the Mini-
assembler to store your program. Do this by typing the address
followed by a colon.

After the colon, type the mnemonic for the first instruction in your
program, followed by a space and the operand of the i nstruction
(formats for operands are listed Table 5-1 ). Now press [ RETURN | .
The Mini-assembler converts the line you typed into hexadecimal,
stores it in memory beginning at the location of the Program
Counter, and then disassembles it again and displays the
disassembled line. It then displays a prompt on the next line.

Now the Mini-assembler is ready to accept the second instruction
in your program. To tell it that you want the next instruction to
follow the first, don't type an address or a colon: just type a
space and the n ext instruction's mnemonic and operand, then
press | return | . The Mini-assembler assembles that line and waits
for another.

If the line you type has an error in it, the Mini-assembler beeps
loudly and displays a circumflex (*) under or near the offending
character in the input line. Most common errors are the result of
typographical mistakes: misspelled mnemonics, missing
parentheses, and so forth. The Mini-assembler also rejects the
input line if you forget the space before or after a mnemonic or
include an extraneous character in a hexadecimal value or
address. If the destination address of a branch instruction is out
of the range of the branch (more than 1 27 locations distant from
the address of the instruction), the Mini-assembler flags this as
an error.

The Mini-assembler

!300:LDX #02

0300- A2 02

LDX

*$02

! LDA $0,X

0302- BB 00

LDA

$00, X

! STA $10,X

0304- 95 10

STA

$10,X

! DEX

0306- CA

DEX

! STA $C030

0307- 8D 30 CO

STA

$C030

! BPL $302

030A- 10 FG

BPL

$0302

! BRK

030C- 00
i

BRK

There are two ways to leave the Mini-assembler and re-enter the
Monitor. One way is to type the Monitor command, FF69G,
preceded by a dollar sign:

!$FF69G

Another way to leave the Mini-assembler is to press | control
| RESET| , which warm-starts BASIC, then type

CALL-151

Using the Monitor

Your assembly language program is now stored in memory. You
can display it with the list command:

•300L

-4

0300-

LDX

*$02

0302-

LDA

$00, X

0304-

STA

$10, X

0306-

DEX

0307-

30 CO

STA

$C030

030A-

BPL

$0302

030C-

BRK

030D-

BRK

030E-

BRK

030F-

BRK

0310-

BRK

0311 -

BRK

0312-

BRK

0313-

BRK

0314-

BRK

0315-

BRK

0316-

BRK

0317-

BRK

0318-

BRK

0319-

BRK

Mini-assembler Instruction Formats

The Apple Mini-assembler recognizes 56 mnemonics and 13
addressing formats used in 6502 assembly-language
programming. The mnemonics are standard, as used in the
Synertek Programming Manual (Apple part number A2L0003), but
the addressing formats are somewhat different. Table 5-1 shows
the Apple standard address-mode formats for 6502 assembly
language.

An address consists of one or more hexadecimal digits. The
Mini-assembler interprets addresses the same way the Monitor
does: if an address has fewer than four digits, the Mini-assembler
adds leading zeros; if the address has more than four digits, then
it uses only the last four.

In this book, dollar signs ($) in addresses signify that the addresses
are in hexadecimal notation. They are ignored by the Mini-
assembler and may be omitted when typing programs.

There is no syntactical distinction between the absolute and zero-
page addressing modes. If you give an instruction to the Mini-
assembler that can be used in both absolute and zero-page
mode, the Mini-assembler assembles that instruction in absolute
mode if the operand for that instruction is greater than $ff, and it
assembles it in zero-page mode if the operand is less than $1 oo.

The Mini-assembler

113

Table 5-1

Formats

Mini-assembler Address

Addressing Mode

Format

Notes

"Note: Accumulator and
Implied-address instructions have no
operands.

Accumulator

Implied

Immediate

*${value}

Absolute

${address}

Zero page

${address}

Indexed zero page

♦{address}, X
${address}, Y

Indexed absolute

${address}, x
${address}, Y

Relative

*{address}

Indexed indirect

(${address}, x)

Indirect indexed

(${address}), Y

Absolute indirect

(${address})

Instructions in accumulator mode and implied addressing mode
need no operands.

Branch instructions, which use the relative addressing mode,
require the target address of the branch. The Mini-assembler
calculates the relative distance to use in the instruction
automatically. If the target address is more than 127 locations
distant from the instruction, the Mini-assembler sounds a bell
(beep), displays a circumflex ( A ) under the target address, and
does not assemble the line.

If you give the Mini-assembler the mnemonic for an instruction
and an operand, and the addressing mode of the operand cannot
be used with the instruction you entered, the Mini-assembler will
not accept the line.

114

Using the Monitor

,„*

■ 4

Summary of Monitor Commands

Here is a summary of the Monitor commands, showing the
syntax diagram for each one. The Mini-assembler commands are
included, even though they are only available when Integer
BASIC is active (see the section "The Mini-assembler").

Examining Memory

{adrs}

{adrs1}.{adrs2}

RETURN

Examines the value contained
in one location.

Displays the values contained
in all locations between
{adrsl} and {adrs2}.

Displays the values in up to
eight locations following the
last opened location.

Changing the Contents of Memory

{adrs}:{val} {val}...

:{val}{val}...

Stores the values in
consecutive memory locations
starting at {adrs}.

Stores values in memory
starting at the next changeable
location.

■ ...

Moving and Comparing

{dest}<{start}.{end}M

{dest}<{start}.{end}V

Copies the values in the range
{start}. {end} into the range
beginning at {dest}.

Compares the values in the
range {start}. {end} to those in
the range beginning at {dest}.

Summary of Monitor Commands

■* -4 C

The Register Command

CONTROL -E

Displays the locations where
the contents of the 6502's
registers are stored and opens
them for changing.

Cassette Tape Commands

{start}.{end}w

{start}. {end}R

Writes the values in the
memory range {start}. {end}
onto tape, preceded by a ten-
second leader.

Reads values from tape,
storing them in memory
beginning at {start} and
stopping at {end}. Prints "ERR'
if an error occurs.

Miscellaneous Monitor Commands

1 CONTROL | -B
[ CONTROL |-C

{val} + {val}
{val}-{val}

Sets Inverse display mode.

Sets Normal display mode.

Enters the language currently
active (usually Applesoft).

Returns to the language
currently active (usually
Applesoft).

Adds the two values and prints
the hexadecimal result.

Subtracts the second value
from the first and prints the
result.

116

Using the Monitor

{slot} [ control] -p

CONTROL

Diverts output to the device
whose interface card is in slot
number {slot}. If {slot}=0,
accepts input from the
keyboard.

Jumps to the machine
language subroutine at location

$3F8.

Running and Listing Programs

{adrs}G

{adrs}L

Transfers control to the
machine language program
beginning at {adrs}.

Disassembles and displays 20
instructions, starting at {adrs}.
Subsequent L's display 20
more instructions.

The Mini-assembler is only available
when Integer BASIC is active.

The Mini-assembler

F666G

$ {command}

*FF69G

Invokes the Mini-assembler.

Executes a Monitor command
from the Mini-assembler.

Leaves the Mini-assembler.

Summary of Monitor Commands

117

Chapter 6

Programming for
Peripheral Cards

121 Peripheral-card Memory Spaces

122 Peripheral-card I/O Space

122 Peripheral-card ROM Space

123 Expansion ROM Space

125 Peripheral-card RAM Space

126 I/O Programming Suggestions

127 Finding the Slot Number

127 I/O Addressing

128 RAM Addressing

129 Changing the Standard I/O Links
131 Using Interrupts

131 Other Uses of I/O Memory Space

132 Switching I/O Memory

Programming for Peripheral Cards

119

Chapter 6

Programming for
Peripheral Cards

The seven expansion slots on the Apple lie's main circuit board
are used for installing circuit cards containing the hardware and
firmware needed to interface peripheral devices to the Apple lie.
These slots are not simple I/O ports; peripheral cards can
access the Apple lie's data, address, and control lines via these
slots. The expansion slots are numbered from 1 to 7, and certain
signals, described below, are used to select a specific slot.

The older Apple II and Apple II Plus models have an eighth
expansion slot: slot number 0. On those models, slot is normally
used for a language card or a ROM card; the functions of the
Apple II Language Card are built into the main circuit board of the
Apple lie.

Peripheral-card Memory Spaces

Because the Apple lie's 6502 microprocessor does all of its I/O
through memory locations, portions of the Apple lie's memory
space have been allocated for the exclusive use of the cards in
the expansion slots. In addition to the memory locations used for
actual I/O, there are memory spaces available for programmable
memory (RAM) in the main memory and for read-only memory
(ROM or PROM) on the peripheral cards themselves.

The memory spaces allocated for the peripheral cards are
described below. Those memory spaces are used for small
dedicated programs such as I/O drivers. Peripheral cards that
contain their own driver routines in firmware like this are called
intelligent peripherals. They make it possible for you to add
peripheral hardware to your Apple Me without having to change
your programs, provided that your programs follow normal
practice for data input and output.

Peripheral-card Memory Spaces

121

Peripheral-card HO Space

Each expansion slot has the exclusive use of sixteen memory
locations for data input and output in the memory space
beginning at location $C090. Slot 1 uses locations $C090 through
$C09F, slot 2 uses locations *coao through $coaf, and so on
through location $C0FF, as shown in Table 6-1.

These memory locations are used for different I/O functions,
depending on the design of each peripheral card. Whenever the
Apple He addresses one of the sixteen I/O locations allocated to
a particular slot, the signal on pin 41 of that slot, called DEVICE
SELECT' , switches to the active (low) state. This signal can be
used to enable logic on the peripheral card that uses the four
low-order address lines to determine which of its sixteen I/O
locations is being accessed.

Table 6-1 Peripheral-card I/O
Memory Locations

Note: The enabling signal is marked
with a prime, to indicate that it is an
active-low signal.

Slot

Locations

Enabled by

$C090-*C09F

DEVICE SELECT'

*C0A0-*C0AF

DEVICE SELECT'

$C0BO-*COBF

DEVICE SELECT'

$C0C0-*C0CF

DEVICE SELECT'

$C0D0-$C0DF

DEVICE SELECT'

$C0E0-*C0EF

DEVICE SELECT'

$C0F0-$C0FF

DEVICE SELECT'

Peripheral-card ROM Space

One 256-byte page of memory space is allocated to each
peripheral card. This space is normally used for read-only
memory (ROM or PROM) on the card with driver programs that
control the operation of the peripheral device connected to the
card.

The page of memory allocated to each expansion slot begins at
location $CnOO, where n is the slot number, as shown in Table 6-2
and Figure 6-3. Whenever the Apple Me addresses one of the

122

Programming for Peripheral Cards

256 ROM memory locations allocated to a particular slot, the
signal on pin 1 of that slot, called I/O SELECT', switches to the
active (low) state. This signal enables the ROM or PROM
devices on the card, and the eight low-order address lines
determine which of the 256 memory locations is being accessed.

■

Table 6-2 Peripheral-card ROM
Memory Locations

Note: The enabling signal is marked
with a prime, to indicate that it is an
active-low signal.

Slot

Locations

Enabled by

*C100-$C1FF

I/O SELECT

*C200-*C2FF

I/O SELECT'

*C300-*C3FF

I/O SELECT

$C400-*C4FF

I/O SELECT'

*CS00-*C5FF

I/O SELECT'

*C600-$C6FF

I/O SELECT'

*C700-*C7FF

I/O SELECT'

If there is an 80-column text card installed in the auxiliary slot, some
of the functions normally associated with slot 3 are performed by
the 80-column text card and the built-in 80-column firmware. With a
80-column text card installed, the I/O select' signal is not available
for slot 3, so firmware in ROM on a card in slot 3 will not run.

Expansion ROM Space

In addition to the small areas of ROM memory allocated to each
expansion slot, peripheral cards can use the 2K-byte memory
space from $C800 to *CFFF for larger programs in ROM or PROM.
This memory space is called expansion ROM space (see the
memory map in Figure 6-3). Besides being larger, the expansion
ROM memory space is always at the same locations regardless
of which slot is occupied by the card, making programs that
occupy this memory space easier to write. (See the section "I/O
Programming Suggestions", below.)

This memory space is available to any peripheral card that needs
it. More than one peripheral card can have expansion ROM on it,
but only one of them can be active at a time.

Peripheral-card Memory Spaces

123

Each peripheral card that uses expansion ROM must have a
circuit on it to enable the ROM. The circuit does this by a two-
stage process: first, it sets a flip-flop when the I/O SELECT' signal,
pin 1 on the slot, becomes active (low); second, it enables the
expansion ROM devices when the I/O strobe' signal, pin 20 on
the slot, becomes active (low). Figure 6-1 shows a typical ROM-
enable circuit.

The i/o select' signal on a particular slot becomes active
whenever the Apple lie's 6502 microprocessor addresses a
location in the 256-byte ROM address space allocated to that
slot. The i/o strobe' signal on all of the expansion slots becomes
active (low) when the 6502 addresses a location in the
expansion-ROM memory space, $C800-$CFFF. The I/O STROBE'
signal is used to enable the expansion-ROM devices on a
peripheral card (see Figure 6-1).

If there is an 80-column text card installed in the auxiliary slot, some
of the functions normally associated with slot 3 are performed by
the text card and the built-in 80-column firmware. With the text card
installed, the I/O strobe' signal is not available on slot 3, so firmware
in expansion ROM on a card in slot 3 will not run.

Figure 6-1 Expansion ROM Enable
Circuit

(\ O SELECt")-

$CFFF'

I/O STROBE

ADDRESS

>
>
>

LATCH
R

ENABLE 1

ENABLE 2

A0 TO A10

A program on a peripheral card can get exclusive use of the
expansion ROM memory space by referring to location $CFFF in
its initialization phase. This location is special: all peripheral cards
that use expansion ROM must recognize a reference to *cfff as
a signal to reset their ROM-enable flip-flops and disable their
expansion ROMs. Of course, doing so also disables the
expansion ROM on the card that is about to use it, but the next
instruction in the initialization code sets the flip-flop on the
expansion-ROM enable circuit on the card. Once this has been
done, this card has exclusive use of the expansion memory
space and its program can jump directly into the expansion
ROM.

As described above, the expansion-ROM disable circuit resets
the enable flip-flop whenever the 6502 addresses location $CFFF.

124

Programming for Peripheral Cards

Figure 6-2 ROM Disable Address
Decoding

A10

I/O STROBE

To RESET, ROM enable
flip-flop

To do this, the peripheral card must detect the presence of *cfff
on the address bus. You can use the I/O STROBE' signal for part
of the address decoding, since it is active for addresses from
$C800 through $cfff. If you can afford to sacrifice some ROM
space, your can simplify the address decoding even further and
save circuitry on the card. For example, if you give up the last
256 bytes of expansion ROM space, your disable circuit only
needs to detect addresses of the form $CFxx, and you can use
the minimal disable-decoding circuitry shown in Figure 6-2.

Table 6-3 Peripheral-card RAM
Memory Locations

"Note: The RAM locations normally
allocated to slot 3 are taken over by
any card installed in the auxiliary slot.

Peripheral-card RAM Space

There are 56 bytes of main memory allocated to the peripheral
cards, eight bytes per card, as shown in Table 6-3. These 56
locations are actually in the RAM memory reserved for the text
and low-resolution graphics displays, but these particular
locations are not displayed on the screen and their contents are
not changed by the built-in output routine C0UT1 . Programs in
ROM on peripheral cards use these locations for temporary data
storage.

Base
Address

Slot Number
3* 4

$0478

$0479

$047A

$047B*

$047C

$047D

$047E

$047F

$04F8

$04F9

$04FA

$04FB*

$04FC

$04FD

$04FE

$04FF

$0578

$0579

$057A

$057B*

$057C

$057D

$057E

$057F

$05F8

$05F9

$05FA

$05FB»

$05FC

$05FD

$05FE

$05FF

$0678

$0679

$067A

$067B»

$067C

$067D

$067E

$067F

$0GF8

$06F9

$06FA

$06FB*

$06FC

$06FD

$06FE

$06FF

$0778

$0779

$077A

$077B*

$077C

$077D

$077E

$077F

$07F8

$07F9

$07FA

$07FB*

$07FC

$07FD

$07FE

$07FF

Peripheral-card Memory Spaces

125

A program on a peripheral card can use the eight base
addresses shown in the table to access the eight RAM locations
allocated for its use, as shown in the next section, "I/O
Programming Suggestions".

I/O Programming Suggestions

A program in ROM on a peripheral card should work no matter
which slot the card occupies. If the program includes a jump to
an absolute location in one of the 256-byte memory spaces, then
the card will only work when it is plugged into the slot that uses
that memory space. If you are writing the program for a
peripheral card that will be used by many people, you should
avoid placing such a restriction on the use of the card.

To function properly no matter which slot a peripheral card is
installed in, the program in the card's 256-byte memory space must
not make any absolute references to itself. Instead of using jump
instructions, you should force conditions on branch instructions,
which use relative addressing.

The first thing a peripheral-card subroutine should do is to save
the contents of the 6502's registers. One way to do this is to use
the monitor subroutine IOSAVE. This subroutine, which starts at
location $FF4A, stores the registers in zero-page memory locations
$45-*49. A companion subroutine, IDREST, restores the registers
from these memory locations. Your program should call I ORE ST,
which starts at location $FF3F, just before it returns control to the
program that called it.

This method of saving the registers is convenient, but it is not
always safe. If a second subroutine calls idsave, or if an interrupt
occurs, the new register contents get saved in the same
locations, and the old ones get destroyed. It is safer, though
somewhat slower, to save the registers on the stack, and restore
them just before returning control to the calling program.

Most single-character I/O is done via the 6502's accumulator. A
character being output through your subroutine will be in the
accumulator with its high bit set when your subroutine is called.
Likewise, if your subroutine is performing character input, it must
leave the character in the accumulator with its high bit set when
it returns to the calling program.

u~.

126 Programming for Peripheral Cards

■

Finding the Slot Number

The memory addresses used by a program on a peripheral card
differ depending on which expansion slot the card is installed in.
Before it can refer to any of those addresses, the program must
somehow determine the correct slot number. One way to do this
is to execute a JSR (Jump to Subroutine) to a location with an RTS
(Return from Subroutine) instruction in it, and then derive the slot
number from the return address saved on the stack, as shown in
the following example.

■

PHP

SEI

JSR $FF58

TSX

LDA $0100, X

AND #$0F

PLP

save status

inhibit interrupts

-> a known RTS instruction

get high byte of the...

...return address from stack

low-order digit is slot no.

restore status

...J

The slot number can now be used in addressing the memory
allocated to the peripheral card, as shown below.

I/O Addressing

Once your peripheral-card program has the slot number, it can
use it to address the I/O locations allocated to the slot. Table 6-4
shows how these locations are related to sixteen base addresses
starting with *C080. Notice that the difference between the base
address and the desired I/O location has the form *n0, where n
is the slot number. Starting with the slot number in the
accumulator, the following example computes this difference by
four left shifts, then loads it into an index register and uses the
base address to specify one of sixteen I/O locations.

ASL
ASL
ASL
ASL
TAX
LDA *C080,X

get n into . . .

. . . hiqh-order nybble...

... of index register.

load from first I/D location

You must make sure that you get an appropriate value into the
index register when you address I/O locations this way. For
example, starting with 1 in the accumulator, the instructions in the
above example perform an lda from location *C090, the first I/O
location allocated to slot 1. If the value in the accumulator had been
0, the LDA would have accessed location $C080, thereby setting the
soft switch that selects the second bank of RAM at location $D000
and enables it for reading (see Chapter 5).

I/O Programming Suggestions

127

Table 6-4 Peripheral-card I/O Base
Addresses

Base
Address

Connector Number
3 4 5

$C080

*C090

*C0A0

*C0B0

$C0C0

*C0D0

*C0E0

$C0F0

*C081

«C091

$C0A1

$C0B1

*C0C1

*C0D1

*C0E1

*C0F1

*C082

$C092

JC0A2

*C0B2

*C0C2

JC0D2

*C0E2

*C0F2

*C083

*C093

*C0A3

*C0B3

$C0C3

*C0D3

$C0E3

*C0F3

$C084

*C094

*C0A4

*C0B4

$C0C4

$C0D4

$C0E4

*C0F4

*C085

$C095

*C0A5

*C0B5

$C0C5

*C0D5

$C0E5

$C0F5

$C086

$C096

*C0AS

IC0B6

*C0C6

$C0DG

*C0E6

*C0F6

*C087

*C097

*C0A7

SC0B7

*C0C7

*C0D7

SC0E7

*C0F7

*C088

*C098

*C0A8

$C0B8

*C0C8

*C0D8

$C0E8

*C0F8

SC089

«C099

*C0A9

*C0B9

$C0C9

*C0D9

*C0E9

$C0F9

*C08A

*C09A

$C0AA

*C0BA

*C0CA

*C0DA

*C0EA

*C0FA

SC08B

*C09B

*C0AB

tCOBB

*C0CB

$C0DB

$C0EB

SCOFB

*C08C

*C09C

*C0AC

$C0BC

*C0CC

*C0DC

*C0EC

$C0FC

»C08D

*C09D

*C0AD

SCOBD

*C0CD

*C0DD

$C0ED

$C0FD

$C08E

*C09E

$C0AE

*C0BE

*C0CE

*C0DE

*C0EE

»C0FE

*C08F

*C09F

$C0AF

$C0BF

*C0CF

*C0DF

$C0EF

$C0FF

RAM Addressing

A program on a peripheral card can use the eight base
addresses shown in Table 6-3 to access the eight RAM locations
allocated for its use. The program does this by putting its slot
number into the Y index register and using indexed addressing
mode with the base addresses. The base addresses can be
defined as constants because they are the same no matter which
slot the peripheral card occupies.

If you start with the correct slot number in the accumulator (by
using the example shown earlier), the following example uses all
eight RAM locations allocated to the slot.

128

Programming for Peripheral Cards

TAY
LDA
STA
LDA
STA
LDA
STA
LDA
STA

$0478, Y
$04F8,Y
$0578, Y
$05F8,Y
$0678, Y
$06F8,Y
$0778, Y
$07F8,Y

Warning

Peripheral-card programs must not store data at the base-address
locations themselves; the RAM at those locations is used by the
Disk Operating System. DOS stores the first byte of the ROM
location of the expansion slot that is currently active ($Cn) in
location $7F8, and the first byte of the ROM location of the slot
holding the controller card for the startup disk drive in location $5F8.

Changing the Standard I/O Links

There are two pairs of locations in the Apple lie that are used for
controlling character input and output. They are called the I/O
links (see Chapter 3). In a Apple lie running without a Disk
Operating System, the I/O links normally contain the starting
addresses of the standard input and output routines key in and
CDUT1 . If a disk operating system is running, one or both of the
links will hold the addresses of the DOS input and output
routines.

The link at locations $38 and $37 (decimal 54 and 55) is called csw,
for Character output Switch. Individually, location $38 is called
CSWL (csw Low) and location $37 is called cswh (csw High). This link
holds the starting address of the subroutine the Apple Me is
currently using for single-character output. This address is
normally $fdfo, the address of routine C0UT1 , described in
Chapter 3.

When you issue a PR'n from BASIC or an n | CONTROL | -P from the
Monitor, the Apple lie changes this link address to the first
address in the ROM memory space allocated to slot number n.
That address has the form $Cn0 0. Subsequent calls for character
output are thus transferred to the program on the peripheral card.
That program can use the instruction sequences given above to
find its slot number and use the I/O and RAM locations allocated
to it. When it is finished, the program can execute an RTS (Return

I/O Programming Suggestions

129

from Subroutine) instruction to return control to the calling
program, or jump to the output routine CDUT1 at location *FDF0 to
display the output character (which must be in the accumulator)
on the screen, then let C0UT1 return to the calling program.

A similar link at locations *38 and *39 (decimal 56 and 57) is
called KSW, for Keyboard input Switch. Individually, location $38 is
called KSWL (for KSW Low) and location $39 is called K5WH(KSW High).
This link holds the starting address of the routine currently being
used for single-character input. This address is normally *FD1B,
the starting address of the standard input routine KEY IN (see
Chapter 3).

When you issue an iN'n command from BASIC or an
n [ CONTROL ]-K from the monitor, the Apple Me changes this
link address to *CnOO, the beginning of the ROM memory space
that is allocated to slot number n. Subsequent calls for character
input are thus transferred to the program on the peripheral card.
That program can use the instruction sequences given above to
find its slot number and use the I/O and RAM locations allocated
to it. The program should put the input character, with its high bit
set, into the accumulator and execute an RTS (Return from
Subroutine) instruction to return control to the program that
requested input.

When the Disk Operating System (DOS) is running, one or both
of the standard I/O links hold addresses of the Disk Operating
System's input and output routines. The DOS has internal
locations that hold the addresses of the character input and
output routines that are currently active.

If a program that is running with DOS changes the standard link
addresses, either directly or via IN' and PR* commands, DOS is
disconnected from the system.

To avoid disconnecting DOS each time they initiate I/O to a slot,
BASIC programs that run with DOS must always issue an IN# or
a PR* command from inside a PRINT statement that starts with a
[control "I -D character. For assembly-language programs, there is
a DOS subroutine call to use when changing the link addresses.
After changing CSW or KSW, the program calls this subroutine at
location *3EA (decimal 1 002). The subroutine transfers the link
address to a location inside DOS and then restores the DOS
address in the standard link location. Refer to the section on
input and output link registers in the DOS Manual for further
details.

130

Programming for Peripheral Cards

Using Interrupts

Although programs running on the Apple Me do not normally use
interrupts, it is possible to do so. To use interrupts on the
Apple lie, your peripheral card must be able to send an interrupt
request (IRQ') to the 6502 microprocessor, and you must store
the address of your interrupt-handling routine in the user interrupt
vector, as described below.

Interrupt priority is handled by a daisy-chain arrangement using
two pins, INT IN and INT out, on each expansion slot. As
described in Chapter 7, each peripheral card breaks the chain
when it makes an interrupt request. On peripheral cards that
don't use interrupts, these pins should be connected together.
The daisy chain gives priority to the peripheral card in slot 7: if
this card opens the connection between INT IN and INT OUT, or if
there is no card in this slot, interrupt requests from cards in slots
1 through 6 can't get through. Similarly, slot 6 controls IRQ from
slots 1 through 5, and so on down the line.

When the IRQ' line on the 6502 microprocessor is activated
(pulled low), the 6502 transfers control through the vector in
locations *fffe-$ffff. This vector is the address of the Monitor's
interrupt handler, which determines whether the request is due to
an external IRQ or a BRK instruction and transfers control to the
appropriate routine via the vectors stored in memory page 3. The
BRK vector is in locations *3F0-*3F1 and the IRQ vector is in
locations *3FE-*3FF (see Table 4-10). The Monitor normally stores
the address of its reset routine in the IRQ vector; you should
substitute the address of your program's interrupt-handling
routine.

Other Uses of I/O Memory Space

The portion of memory space from location JC000 through $CFFF
(decimal 491 52 through 53247) is normally allocated to I/O and
program memory on the peripheral cards, but there are two other
functions that also use this memory space: the built-in self-test
firmware and the 80-column display firmware. The soft switches
that control the allocation of this memory space are described
below.

Other Uses of I/O Memory Space

131

Figure 6-3 I/O Memory Map

CFFF

C800
C700
C600
C500
C400
C300
C200
C100

cooo

PERIPHERAL

EXPANSION

ROM

INTERNAL

ROM

AND

PERIPHERAL

EXPANSION

ROM

INTERNAL
ROM

SLOT #7 ROM

SLOT #6 ROM

SLOT #5 ROM

SLOT #4 ROM

SLOT #3 ROM

INTERNAL ROM

SLOT #2 ROM

SLOT #1 ROM

INTERNAL SOFT SWITCHES AND PERIPHERAL I/O

Switching 110 Memory

The built-in firmware uses two soft switches to control the
allocation of the I/O memory space from $C000 to *cfff. The

1
9

j^ i

locations of these soft switches
given in Table 6-5.

SLDTCXROM and SL0TC3R0M, are

Like the display switches described in Chapter 2, these soft switches
share their locations with the keyboard data and strobe functions.
The switches are activated only by writing, and the states can be
determined only by reading, as indicated in Table 6-5.

When SL0TC3R0M is on, the 256-byte ROM area at *C300 is
available to a peripheral card in slot 3, which is the slot normally
used for a terminal interface. If a card is installed in the auxiliary
slot when you turn on the power or reset the Apple lie, the
SL0T3RDM switch is turned off. Turning SL0TC3R0M off disables

Programming for Peripheral Cards

&u2

Table 6-5 I/O Memory Switches

Name

Function

Location
Hex Decimal

Notes

SL0TC3R0M Slot ROM at $C300 SCOOB 49163 -16373 Write

Internal ROM at $C300 *C00A 49162 -16374 Write

Read SL0TC3R0M switch $C017 49175 -16361 Read

SLOTCXROM Slot ROM at *CxOO $C007 49159 -16377 Write

Internal ROM at *CxOO *C006 49158 -16378 Write

Read SLQTCXROM switch JC015 49173 -16363 Read

peripheral-card ROM in slot 3 and enables the built-in 80-column
firmware, as shown in Figure 6-3. The 80-column firmware is
assigned to slot-3 address space because slot 3 is normally used
with a terminal interface, so the built-in firmware will work with
programs that use slot 3 this way.

Installing an 80-column text card in the auxiliary slot makes it
impossible to run any peripheral card that has built-in firmware in
slot 3. If an 80-column text card is not installed, a peripheral card in
slot 3 will work properly.

The bus and I/O signals are always available to a peripheral
card in slot 3, even when the 80-column hardware and firmware
are operating. Thus it is always possible to use this slot for any
I/O accessory that does not have built-in firmware.

When SLOTCXROM is active (high), the I/O memory space from
*C1 00 to *C7FF is allocated to the expansion slots, as described
previously. Setting slotcxrom inactive (low) disables the peripheral-
card ROM and selects built-in ROM in all of the I/O memory
space except the part from *C000 to *C0FF (used for soft switches
and data I/O), as shown in Figure 6-3. In addition to the 80-
column firmware at *C300 and *C800, the built-in ROM includes
firmware that performs the self-test of the Apple lie's hardware.

Setting SLOTCXROM low enables built-in ROM in all of the I/O memory
space (except the soft-switch area), including the $C300 space, which
contains the 80-column firmware.

Other Uses of I/O Memory Space

137 Environmental Specifications

138 The Power Supply

139 The Power Connector

140 The 6502 Microprocessor

141 6502 Timing

143 The Custom Integrated Circuits
143 The Memory Management Unit
1 45 The Input/Output Unit

147 The PAL Circuit

148 Memory Addressing

148 ROM Addressing

149 RAM Addressing

149 Dynamic-RAM Refreshment

151 Dynamic-RAM Timing

152 The Video Display

153 The Video Counters

154 Display Memory Addressing
154 Display Address Mapping
1 58 Video Display Modes

158 Text Displays

160 Low-resolution Display

161 High-resolution Display

163 Video Output Signals

164 Built-in I/O Circuits

164 The Keyboard

165 Connecting a Keypad

166 Cassette I/O

166 The Speaker

167 Game I/O Signals

Uj^

134

Hardware Implementation

Chapter 7

Hardware Implementation

169 Expanding the Apple Me

169 The Expansion Slots

169 The Peripheral Address Bus

170 The Peripheral Data Bus
170 Loading and Driving Rules

170 Interrupt and DMA Daisy Chains

174 Video Signals on Slot 7

174 The Auxiliary Slot

175 80-column Display Signals

Hardware Implementation

135

Chapter 7

Hardware Implementation

Most of this manual describes functions — what the Apple lie
does. This chapter, on the other hand, describes objects: the
pieces of hardware the Apple lie uses to carry out its functions.
If you are designing a piece of peripheral hardware to attach to
the Apple lie, or if you just want to know more about how the
Apple lie is built, you should study this chapter.

Environmental Specifications

The Apple lie is quite sturdy when used in the way it was
intended. Table 7-1 defines the conditions under which the
Apple lie is designed to function properly.

IS Table 7-1 Summary of Environmental

Specifications

Operating Temperature: 0° to 45°C (30° to 1 1 5°F)
Relative Humidity: 5% to 85%

Line Voltage : 1 07 to 1 32 VAC

I
mm — -*

You should treat the Apple lie with the same kind of care as any
other electrical appliance. You should protect it from physical
violence, such as hammer blows or defenestration. You should
protect the mechanical keyboard and the electrical connectors
inside the case from spilled liquids, especially those with
dissolved contaminants, such as coffee and cola drinks.

In normal operation, enough air flows through the slots in the
case to keep the insides from getting too hot, although some of
the parts inside the Apple lie normally get rather warm to the
touch. If you manage to overheat your Apple lie, by blocking the
ventilation slots in the top and bottom for example, the first
symptom will be erratic operation. The memory devices in the
Apple lie are sensitive to heat: when they get too hot, they

Environmental Specifications

137

occasionally change a bit of data. The exact result .depends on
what kind of program you are running and on just which bit of
memory is affected.

The Power Supply

The power supply in the Apple Me operates on normal household
AC power and provides enough low-voltage electrical power
for the built-in electronics plus a full complement of peripheral
cards, including disk controller cards and communications
interfaces. The basic specifications of the power supply are listed
in Table 7-2.

The Apple He's power cord should be plugged into a three-wire
1 10- to 120-volt outlet. You must connect the Apple Me to a
grounded outlet or to a good earth ground. Also, the line voltage
must be in the range given in Table 7-2. If you try to operate the
Apple lie from a power source with more than 140 volts, you will
damage the power supply.

Table 7-2 Power Supply

Line voltage:

107V to 132V AC

Specifications

'Intermittent operation: The Apple lie

Maximum power consumption:

60W continuous
80W intermittent*

can safely operate for up to twenty
minutes at the higher load if followed

Supply voltages:

+5V ±3%

by at least ten minutes at normal
load.

+ 11.8V ±6%
-5.2V ±10%
-12V ±10%

Maximum supply currents:

+5V:2.5A
+ 12V: 1.5A continuous,
2.5A intermittent

-5V: 250mA
-12V: 250mA

Maximum case temperature:

55°C(130°F)

The Apple Me uses a custom-designed switching-type power
supply. It is small and lightweight, and it generates less heat than
other types of power supplies do.

The Apple He's power supply works by converting the AC line
voltage to DC and using this DC voltage to power a variable-
frequency oscillator. The oscillator drives a small transformer with
many separate windings to produce the different voltages
required. A circuit compares the voltage of the +5-volt supply
with a reference voltage and feeds an error signal back to the

138

Hardware Implementation

Table 7-3 Power Connector Signal
Specifications

oscillator circuit. The oscillator circuit uses the error signal to
control the frequency of its oscillation and keep the output
voltages in their normal ranges.

The power supply includes circuitry to protect itself and the other
electronic parts of the Apple Me by turning off all four supply
voltages whenever it detects one of the following malfunctions:

• any supply voltage short-circuited to ground;

• the power-supply cable disconnected;

• any supply voltage outside the normal range.

Any time one of these malfunctions occurs, the protection circuit
stops the oscillator, and all the output voltages drop to zero. After
about half a second, the oscillator starts up again. If the
malfunction is still occurring, the protection circuit stops the
oscillator again. The power supply will continue to start and stop
this way until the malfunction is corrected or the power is turned
off.

Warning

If you think the power supply is broken, do not attempt to repair it
yourself. The power supply is in a sealed enclosure because some
of its circuits are connected directly to the power line. Special
equipment is needed to repair the power supply safely, so see your
Apple dealer for service.

The Power Connector

The cable from the power supply is connected to the main circuit
board by a six-pin connector with a strain-relief catch. The
connector pins are identified in Table 7-3 and Figure 7-1 4d.

Pin Number

Name

Description

1,2

Ground

Common electrical ground

+5V

+5V from power supply

+ 12V

+ 12V from power supply

-12V

-12V from power supply

-5V

-5V from power supply

The Power Supply

139

The 6502 Microprocessor

The Apple lie uses a 6502B microprocessor as its central
processing unit (CPU). The 6502B in the Apple lie runs at a
clock rate of 1 .023 MHz and performs up to 500,000 eight-bit
operations per second. You should not use the clock rate as a
criterion for comparing different types of microprocessors. The
6502 has a simpler instruction cycle than most other
microprocessors and it uses instruction pipelining for faster
processing. The speed of the 6502 with a 1MHz clock is
equivalent to other types of microprocessors with clock rates up
to 2.5MHz.

The 6502 has a sixteen-bit address bus, giving it an address
space of 64K (2 to the sixteenth power or 65536) bytes. The
Apple He uses special techniques to address a total of more than
64K: see the sections "Bank-switched Memory" and "Auxiliary
Memory and Firmware" in Chapter 4 and the section "Switching
I/O Memory" in Chapter 6.

Table 7-4 6502 Microprocessor
Specifications

Type:

6502B

Accumulator (A)
Index Registers (X, Y)
Stack Pointer (S)
Processor Status (P)

Eight bits

Data bus:

Eight bits wide

Address bus:

Sixteen bits wide

Address range:

65,536 (64K)

Interrupts:

IRQ (maskable)
NMI (nonmaskable)
BRK (programmed)

Operating voltage:

+ 5V (± 5%)

Power dissipation:

500mW (typical)

L— I

Hardware Implementation

6502 Timing

The operation of the Apple lie is controlled by a set of
synchronous timing signals, sometimes called clock signals. In
electronics, the word clock is used to identify signals that control
the timing of circuit operations. The Apple lie doesn't contain the
kind of clock you tell time by, although its internal timing is
accurate enough that a program running on the Apple lie can
simulate such a clock.

The frequency of the oscillator that generates the master timing
signal is 14.31818 MHz. Circuitry in the Apple Me uses this clock
signal, called 1 4M, to produce all the other timing signals. These
timing signals perform two major tasks: controlling the computing
functions, and generating the video display. The timing signals
directly involved with the operation of the 6502 are described in
this section. Other timing signals are described in the sections
"RAM Addressing", "Video Display Modes", and "The Expansion
Slots".

The main 6502 timing signals are listed in Table 7-5, and their
relationships are diagrammed in Figure 7-1 . The 6502 clock
signals are #1 and </>o, complementary signals at a frequency of
1 .02273 MHz. If you need more information about the 6502 itself,
refer to the Synertek Hardware Manual (Apple product number
A2L0002). The Apple Me signal named </>o is equivalent to the
signal called </>2 in the hardware manual (it isn't identical: it's a
tiny bit early).

Table 7-5 6502 Timing Signal
Descriptions

Signal Name

14M

Description

Master oscillator, 14.31818 MHz; also 80-column dot clock.

Intermediate timing signal and 40-column dot clock.

Intermediate timing signal, 2.04545 MHz with asymmetrical duty
cycle.

Phase of 6502 clock, 1 .022727 MHz; Complement of </>1 .

Phase 1 of 6502 clock, 1 .022727 MHz; Complement of <£0.

The 6502 Microprocessor

Figure 7-1 6502 Timing Signals

14M

nmrwuiJiJinLn^^

490 ns

280 ns

210 ns

CPU phase
— 490 ns -

1-^—110 ns (max) 15 ns (min)-

ADDR
from 6502

30 ns (min)

75 ns (max) — »>
DATA from 6502 (write) ^X ~

50 ns (min)

DATA to 6502 (read)

1 ns (min)

The operations of the 6502 are related to the clock signals in a
simple way: address during </>1, data during <£o. The 6502 puts
an address on the address bus during #1. This address is valid
not later than 110 nanoseconds after </>1 goes high and remains
valid through all of 0o. The 6502 reads or writes data during 4>o.
If the 6502 is writing, the read/write signal is low during </>o and
the 6502 puts data on the data bus. The data is valid not later
than 75 nanoseconds after Oo goes high. If the 6502 is reading,
the read/write signal remains high. Data on the data bus must be
valid no later than 50 nanoseconds before the end of <£o.

142

Hardware Implementation

■M. ;.*,

Figure 7-2 The MMU Pinouts

GND

PRAS'

RAO

RA1

RA2

RA3

RA4

RA5

RA6

RA7

R/W

INH

DMA'

EN80'

KBD'

ROMEN2'

ROMENV

A10

A11

A12

A13

A14

A15

+ 5V

Cxxx

RAMEN'

R/W 245

MD7

The Custom Integrated Circuits

Most of the circuitry that controls memory and I/O addressing in
the Apple He is in three custom integrated circuits called the
Memory Management Unit (MMU), the Input-Output Unit (IOU),
and the Programmed Array Logic device (PAL). The soft switches
used for controlling the various I/O and addressing modes of the
Apple Me are addressable flags inside the MMU and the IOU.
The functions of these two devices are not as independent as
their names suggest; working together, they generate all of the
addressing signals. For example, the MMU generates the
address signals for the CPU, while the IOU generates similar
address signals for the video display.

The Memory Management Unit

The circuitry inside the MMU implements these soft switches,
which are described in the following chapters:

Page 2 display (PAGE2): Chapter 2

Hi-res mode (HIRES): Chapter 2

Store to 80-column card (80STDRE): Chapter 2

Select bank 2: Chapter 4

Enable bank-switched RAM: Chapter 4

Read auxiliary memory (RAMRD): Chapter 4

Write auxiliary memory (RAMWRT): Chapter 4

Auxiliary stack and zero page (altzp): Chapter 4

Slot ROM for connector #3 (SL0TC3RDM): Chapter 6

Slot ROM in I/O space (SLOTCXROM): Chapter 6

The 64K dynamic RAMs used in the Apple lie use a multiplexed
address, as described below in the section "Dynamic-RAM Timing'
The MMU generates this multiplexed address for memory reading
and writing by the 6502 CPU.

The Custom Integrated Circuits

143

Table 7-6 The MMU Signal

Pin Number

Name

Description

Descriptions

GND

Power and signal common

6502 address input

40-26

A1 -A15

6502 address input

</>0

Clock phase

Timing signal

PRAS'

Memory Row-address strobe

6-13

RA0-RA7

Multiplexed address output

1 4

R/W

6502 read-write control signal

INH'

Inhibits main memory

DMA'

Controls data bus for DMA transfers

EN80'

Enables auxiliary RAM

KBD'

Enables keyboard data bit 0-6

R0MEN2'

Enables built-in firmware ROM #2

R0MEN1'

Enables built-in firmware ROM #1

MD7

State of MMU flags

RW'245

Controls 74LS245 data-bus buffer

RAMEN'

Enables main RAM

CXXX

Enables peripheral-card memory

+ 5V

Power

144

Hardware Implementation

Figure 7-3 The IOU Pinouts

GND

SEGA

SEGB

80VID

CASSO

SPKR

MD7

ANO

AN1

AN 2

AN3

R/W

RESET

(n.c.)

RAO

RA1

RA2

RA3

SYNC'

WNDW

CLRGAT

RA10'

RA9'

VID6

VID7

KSTRB

AKD

COxx

+ 5V

PRAS'

RA7

RA6

RA5

RA4

The Input/Output Unit

The circuitry inside the Input/Output Unit (IOU) implements the
following soft switches, all described in Chapter 2:

Page 2 display (PAGE2)

Hi-res mode (HIRES)

Text mode (TEXT)

Mixed mode (MIXED)

80-column display (80COL)

Character-set select (altcharset)

Any-key-down

Annunciators

Vertical blanking (VBL)

The 64K dynamic RAMs used in the Apple lie require a multiplexed
address, as described below in the section "Dynamic-RAM Timing".
The IOU generates this multiplexed address for the data transfers
required for display and memory refresh during clock phase 1. The
way this address is generated is described below in the section
"Video Display Generation".

.-,

The Custom Integrated Circuits

145

Table 7-7 The IOU Signal
Descriptions

Pin Number

Name

Description _^a

Note: Pin 16 is not connected.

GND

Power and signal common

Graphics mode enable |

3,4

SEGA,
SEGB

Display vertical counter bits

80VID'

CASSO

SPKR

MD7

10-13

AN0-AN3

R/N'

RESET'

17-24

RA0-RA7

PRAS'

</>0

+ 5V

COXX'

AKD

KSTRB

33,34

VID7, VIDG

35,36

RA9', RA10'

CLRGAT'

WNDW

SYNC

Display vertical counter bit

80-column video enable

Cassette output signal

Speaker output signal

Internal flags to data bus

Annunciator outputs

6502 read-write control signal

Power on and reset output

Multiplexed RAM address (phase 0)

Row-address strobe (phase 0)

Master clock phase

Intermediate timing signal

Power

Address bit 6 from 6502

I/O address enable

Any-key-down signal

Keyboard strobe signal

Video display control bits

Color-burst gate (enable)

Display blanking signal

Display synchronization signal

Display horizontal timing signal

146

Hardware Implementation

The PAL Circuit

A Programmed Array Logic device, type PAL 16R8, generates
several timing and control signals in the Apple He. These signals
are listed in Table 7-8.

Table 7-8 The PAL Signal
Descriptions

Figure 7-4 The PAL Pinouts

14M

3.58M

VID7

SEGB

RAMEN'

80VID'

GND

1 1

+ 5V

PRAS'

(n.c.)

PCAS'

<t>0

VID7M

LDPS'

ENTMG

Pin Number

Name

Description

14M

14.31818 MHz master liming signal

7.15909 MHz timing signal

3.58M

3.579545 MHz timing signal

Horizontal video timing signal

VID7

Video data bit 7

SEGB

Video timing signal

Video display graphics-mode enable

RAMEN'

RAM enable (CAS enable)

80V ID'

Enable 80-column display mode

GND

Power and signal common

ENTMG

Enable master timing

LDPS'

Video shift-register load enable

VID7M

Video dot clock, 7 or 14 MHz

Phase 1 system clock

<i>0

Phase system clock

Intermediate timing and strobe signal

PCAS'

RAM Column-address strobe

N.C.

(This pin is not used.)

PRAS'

RAM Row-address strobe

+ 5V

Power

The Custom Integrated Circuits

147

Memory Addressing

The 6502 microprocessor can address 65,536 locations. The
Apple He uses this entire address space, and then some: some
areas in memory are used for more than one function. The
following sections describe the memory devices used in the
Apple Me and the way they are addressed. Input and output also
use portions of the memory address space; refer to the section
"Peripheral-card Memory Spaces" in Chapter 6 for information.

ROM Addressing

In the Apple Me, the following programs are permanently stored in
two type 2364 8K by 8-bit ROMs (read-only memory):

• Applesoft editor and interpreter

• Monitor

• 80-column display firmware

• Self-test routines

These two ROMs are enabled by two signals called RDMEN1 and
R0MEN2. The ROM enabled by RDMEN1 , sometimes called the
Diagnostics ROM, occupies the memory address space from
$cioo to $dfff. The address space from $C300 to*C3FF and from
*C800 to $CFFF contains the 80-column display firmware. Those
address spaces are normally assigned to ROM on a peripheral
card in slot 3; for a discussion of the way the 80-column
firmware overrides the peripheral card, see the section "Other
Uses of I/O Memory Space" in Chapter 6.

Two other portions of the Diagnostics ROM, addressed from
$C1 00 to*C2FF andfrom*C400 to $C7FF, contain the built-in self-test
routines. These address spaces are normally assigned to the
peripheral cards; when the self-test programs are running, the
peripheral cards are disabled.

The remainder of the Diagnostics ROM, addressed from *D0 00 to
$dfff, contains part of the Applesoft BASIC interpreter.

The ROM enabled by R0MEN2, sometimes called the Monitor ROM,
occupies the memory address space from $E000 to *ffff. This
ROM contains the rest of the Applesoft interpreter, in the address
space from $E000to$EFFF, and the Monitor subroutines, from

$F000 to JFFFF.

148 Hardware Implementation

■

+ 5V

A12

MDO

MD1

MD2

GND

Figure 7-5 The 2364 ROM Pinouts

+ 5V

A1 1

ROMENx'

A10

CE'

MD7

MD6

MD5

MD4

MD3

Figure 7-6 The 2316 ROM Pinouts

+ 5V

KBD'

GND*

ENKBD'

(n.C.)

MD6

MD5

MD4

MD3

Figure 7-7 The 2333 ROM Pinouts

+ 5V

VID5

RA9

WNDW

RA10

ENVID'

MDO

MD1

MD2

1 1

GND

VID4

VID3

VI D2

VID1

VIDO

5EGB

SEGA

1 1

GND

The other ROMs in the Apple He are a type 2316 ROM used for
the keyboard character decoder and a type 2333 ROM used for
character sets for the video display. This 2333 ROM is rather
large because it includes a section of straight-through bit-
mapping for the graphics modes. This way, graphics display
video can pass through the same circuits as text without
additional switching circuitry.

RAM Addressing

The RAM (programmable) memory in the Apple lie is used both
for program and data storage and for the video display. The
areas in RAM that are used for the display are accessed both by
the 6502 microprocessor and by the video display circuits. In
some computers, this dual access results in addressing conflicts
(cycle stealing) that can cause temporary dropouts in the video
display. This problem does not occur in the Apple lie, thanks to
the way the microprocessor and the video circuits share the
memory.

The memory circuits in the Apple lie take advantage of the two-
phase system clock described in the section "System Timing" to
interleave the microprocessor memory accesses and the display
memory accesses so that they never interfere with each other.
The microprocessor reads or writes to RAM only during </>0, and
the display circuits read data only during 01.

Dynamic-RAM Refreshment

The image on a video display is not permanent; it fades rapidly
and must be refreshed periodically. To refresh the video display,
the Apple lie reads the data in the active display page and sends
it to the display. To prevent visible flicker in the display, and to
conform to standard practice for broadcast video, the Apple lie
refreshes the display sixty times per second.

The dynamic RAM devices used in the Apple Me also need a
kind of refresh, because the data is stored in the form of electric
charges which diminish with time and must be replenished every
so often. The Apple lie is designed so that refreshing the display
also refreshes the dynamic RAMs. The next few paragraphs
explain how this is done.

The job of refreshing the dynamic RAM devices is minimized by
the structure of the devices themselves. The individual data cells
in each RAM device are arranged in a rectangular array of rows

Memory Addressing

149

and columns. When the device is addressed, the part of the
address that specifies a row is presented first, followed by the
address of the column. Splitting information into parts that follow
each other in time is called multiplexing. Since only half of the
address is needed at one time, multiplexing the address reduces
the number of pins needed for connecting the RAMs.

Different manufacturers' 64K RAMs have cell arrays of either 128
rows by 512 columns or 256 rows by 256 columns. Only the row
portion of the address is used in refreshing the RAMs.

Now consider how the display is refreshed. As described later in
this chapter in the section "The Video Counters", the display
circuitry generates a sequence of 8,192 memory addresses in
high-resolution mode; in text and low-resolution modes, this
sequence is the 1 ,024 display-page addresses repeated eight
times. The display address cycles through this sequence 60
times a second, or once every 17 milliseconds. The way the low-
order address lines are assigned to the RAMs, the row address
cycles through all 256 possible values once every half-millisecond
(see Table 7-9). This more than satisfies the refresh
requirements of the dynamic RAMs.

Table 7-9 RAM Address Multiplexing

Figure 7-8 The 64K RAM Pinouts

Mux'd Address

Row Address

Column Address

+ 5V

1 16

MDx

2 15

R/W

3 14

RAS'

4 13

RA7

5 12

RA5

6 11

RA6

7 10

+ 5V

8 9

RAO

RA1

touts

RA2

RA3

GND
CAS'

RA4

MDx
RA1

RA5

RA4

RA6

RA3

RA2

RA7

RAO

A10

A11

A12

A13

A14

A15

150

Hardware Implementation

_- ..

Dynamic-RAM Timing

The Apple lie's microprocessor clock runs at a moderate speed,
about 1 .023 MHz, but the interleaving of CPU and display cycles
means that the RAM is being accessed at a 2 MHz rate, or a
cycle time of just under 500 nanoseconds. Data for the CPU is
strobed by the falling edge of <£o, and display data is strobed by
the falling edge of $1, as shown in Figure 7-9.

Table 7-10 Dynamic RAM Timing
Signals

The RAM timing looks complicated because the RAM address is
multiplexed, as described in the previous section. The MMU
takes care of multiplexing the address for the CPU cycle, and the
IOU performs the same function for the display cycle. The
multiplexed address is sent to the RAM ICs over the lines
labelled RA0-RA7. Along with the other timing signals, the PAL
generates two signals that control the RAM addressing: Row-
address Strobe (RAS) and Column-address Strobe (CAS).

Signal Name

Description

4>0 Clock phase (CPU phase)

</>1 Clock phase 1 (display phase)

RAS Row-address strobe

CAS Column-address strobe

Q3 Alternative column-address strobe

RA0-RA7 Multiplexed address bus

MD0-MD7 Internal data bus

Memory Addressing

151

Figure 7-9 RAM Timing Signals

RA0-RA7

MD0-MD7

0<^>— <ZXZ3

C3-

T/7e Video Display

The Apple Me produces a video signal that creates a display on a
standard video monitor or, if you add an RF modulator, on a
black-and-white or color television set. The video signal is a
composite made up of the data that is being displayed plus the
horizontal and vertical synchronization signals that the video
monitor uses to arrange the lines of display data on the screen.

Apple lie's manufactured for sale in the U.S. generate a video signal
that is compatible with the standards set by the NTSC (National
Television Standards Committee). Apple lie's manufactured for sale
in European countries generate video that is compatible with the
standard used there, which is called PAL (for Phase Alternating
Lines). This manual describes only the NTSC version of the video
circuits.

152

Hardware Implementation

The display portion of the video signal is a time-varying voltage
generated from a stream of data bits, where a one corresponds
to a voltage that generates a bright dot, and a zero to a dark
dot. The display bit stream is generated in bursts that correspond
to the horizontal lines of dots on the video screen. The signal
named wndw is low during these bursts.

During the time intervals between bursts of data, nothing is
displayed on the screen. During these intervals, called the
blanking intervals, the display is blank and the WNDW signal is
high. The synchronization signals, called sync for short, are
produced by making the signal named SYNC low during portions
of the blanking intervals. The sync pulses are at a voltage
equivalent to blacker-than-black video and don't show on the
screen.

The Video Counters

The address and timing signals that control the generation of the
video display are all derived from a chain of counters inside the
IOU. Only a few of these counter signals are accessible from
outside the IOU, but they are all important in understanding the
operation of the display generation process, particularly the
display memory addressing described in the next section.

The horizontal counter is made up of seven stages: ho, m , H2, H3,
H4, hb, and HPE' . The input to the horizontal counter is the 1 MHz
signal that controls the reading of data being displayed. The
complete cycle of the horizontal counter consists of 65 states.
The six bits HO through H5 count normally from to 63, then start
over at 0. Whenever this happens, hpe' forces another count with
HO through H5 held at zero, thus extending the total count to 65.

The IOU uses the forty horizontal count values from 25 through
64 in generating the low-order part of the display data address,
as described below in the section "Display Address Mapping".
The IOU uses the count values from to 24 to generate the
horizontal blanking, the horizontal sync pulse, and the color-burst
gate.

When the horizontal count gets to 65, it signals the end of a line
by triggering the vertical counter. The vertical counter has nine
stages: va, vb, vc, vo, V1 , V2, V3, V4, and vs. When the vertical
count reaches 262, the IOU resets it and starts counting again
from zero. Only the first 192 scanning lines are actually
displayed; the IOU uses the vertical counts from 192 to 261 to

The Video Display

153

generate the vertical blanking and sync pulse. Nothing is
displayed during the vertical blanking interval. (The vertical line
count is 262 rather than the standard 262.5 because, unlike -
normal television, the Apple lie's video display is not interlaced.)

Animation displays sometimes have an erratic flicker caused by
changing the display data at the same time it is being displayed.
You can avoid this on the Apple lie by reading the vertical-blanking
signal (vbl) at location $C019 and only changing display data while
vbl is low (data value less than 128).

Display Memory Addressing

As described in Chapter 2 in the section "Addressing Display
Pages Directly", data bytes are not stored in memory in the
same sequence in which they appear on the display. You can
get an idea of the way the display data is stored by using the
Monitor to set the display to graphics mode, then storing data
starting at the beginning of the display page at hexadecimal *40
and watching the effect on the display. If you do this, you should
use the graphics display instead of text to avoid confusion: the
text display is also used for Monitor input and output.

If you want your program to display data by storing it directly into
the display memory, you must first transform the display
coordinates into the appropriate memory addresses, as shown in
Chapter 2. The descriptions that follow will help you understand
how this address transformation is done and why it is necessary.
They will not (alas!) eliminate that necessity.

The address transformation that folds three rows of forty display
bytes into 128 contiguous memory locations is the same for all
display modes, so it is described first. The differences among the
different display modes are described in the section "Video
Display Modes", below.

Display Address Mapping

Consider the simplest display on the Apple lie, the 40-column
text mode. To address forty columns requires six bits, and to
address twenty-four rows requires another five bits, for a total of
eleven address bits. Addressing the display this way would
involve 2048 (two to the eleventh power) bytes of memory to
display a mere 960 characters. The 80-column text mode would
require 4096 bytes to display 1920 characters. The leftover

154 Hardware Implementation

chunks of memory that were not displayed could be used for
storing other data, but not easily, because they would not be
contiguous.

Instead of using the horizontal and vertical counts to address
memory directly, the circuitry inside the IOU transforms them into
the new address signals described below. The transformed
display address must meet the following criteria:

• Map the 960 bytes of 40-column text into only 1024 bytes.

• Scan the low-order address to refresh the dynamic RAMs.

• Continue to refresh the RAMs during video blanking.

The requirements for RAM refreshing are discussed above, in the
section "Dynamic-RAM Refreshment".

The transformation involves only horizontal counts H3, H4, and H5,
and vertical counts V3 and V4. Vertical count bits VA, vb, and vc
address the lines making up the characters, and are not involved
in the address transformation. The remaining low-order count
bits, HO, H1 , H2, vo, V1 , and V2 are used directly, and are not
involved in the transformation.

The IOU performs an addition that reduces the five significant
count bits to four new signals called so, S1 , S2, and S3, where S
stands for sum. Figure 7-10 is a diagram showing the addition in
binary form, with V3 appearing as the carry in and H5 appearing
as its complement H5 ' . A constant value of one appears as the
low-order bit of the addend. The carry bit generated with the sum
is not used.

Figure 7-10 Display Address
Transformation

Carry in

H5'

Augend

Addend

Sum

If this transformation seems terribly obscure, try it with actual
values. For example, for the upper-left corner of the display, the
vertical count is zero and the horizontal count is 24: HO, H1 , H2,
and H5 are zeros and H3 and H4 are ones. The value of the sum
is zero, so the memory location for the first character on the
display is the first location in the display page, as you might
expect.

The Video Display

155

Horizontal bits ho, hi , and H2 and sum bits SO, S1 , and S2 make up
the transformed horizontal address (AO through A6 in Table 7-11).
As the horizontal count increases from 24 to 63, the value of the
sum (S3 S2 S1 so) increases from zero to four and the transformed
address goes from to 39, relative to the beginning of the
display page.

The low-order three bits of the vertical row counter are vo , V1 ,
and V2. These bits control address bits A7, A8, and A9, as shown
in Table 7-1 1 , so that rows through 7 start on 128-byte
boundaries. When the vertical row counter reaches 8, vo, V1 , and
V2 are zero again, and V3 changes to one. If you do the addition
in Figure 7-10 with H equal to 24 (the horizontal count for the first
column displayed) and v equal to 8, the sum is 5 and the
horizontal address is 40: the first character in row 8 is stored in
the memory location 40 bytes from the beginning of the display
page.

Figure 7-11 40-column Text Display
Memory. Memory locations marked with
an asterisk (*) are reserved for use by
peripheral I/O firmware: refer to the
section "Peripheral-card RAM Space",
in Chapter 6.

^-I

-< — 40 bytes — ►

-* — 40 bytes — *-

-^ — 40 bytes — ►

8
bytes |

$400

row

row 8

row 16

$480

row 1

row 9

row 1 7

$500

row 2

row 10

row 1 8

$580

row 3

row 1 1

row 1 9

$600

row 4

row 1 2

row 20

$680

row 5

row 13

row 21

$700

row 6

row 14

row 22

$780

row 7

row 15

—

row 23

Figure 7-1 1 shows how groups of three forty-character rows are
stored in blocks of 120 contiguous bytes starting on 128-byte
address boundaries. This diagram is another way of describing
the display mapping shown in Figure 2-5. Notice that the three
rows in each block of 120 bytes are not adjacent on the display.

Hardware Implementation

Table 7-11 Display Memory
Addressing

Memory
Address Bit

Display
Address Bit

*For these address bits, see text and
Table 7-12.

A10

A1 1

A12

A13

•

A14

•

A15

GND

Table 7-1 1 shows how the signals from the video counters are
assigned to the address lines. HO, H1 , and H2 are horizontal-count
bits, and vo, vi , and V2 are vertical-count bits, so, S1 , S2 and S3
are the folded address bits described above. Address bits
marked with asterisks (* ) are different for different modes: see
Table 7-12 and the next three sections.

The Video Display

157

Table 7-12 Memory Address Bits for
Display Modes

Address Bit

Display Mode:
Text and Lo-Res Hi-Res

A1
A11
A12
A13
A14

80VID + PG2'
80VID'-PG2

80VID + PG2'

80VID'-PG2

158

Video Display Modes

The different display modes all use the address-mapping scheme
described in the previous section, but they use different-sized
memory areas in different locations. The next three sections
describe the addressing schemes and the methods of generating
the actual video signals for the different display modes.

Text Displays

The text and low-resolution graphics pages begin at memory
locations *400 and *800. Table 7-12 shows how the display-mode
signals control the address bits to produce these addresses.
Address bits A10 and A1 1 are controlled by PG2 and 80VID, which
are set by the display-page and 80-column-video soft switches.
Address bits A1 2, A1 3, and A1 4 are set to zero. Notice that 80VID
active inhibits PG2: there is only one display page in 80-column
mode.

The low-order six bits of each data byte reach the character
generator directly, via the video data bus v I DO - v I ds . The two high-
order bits are modified by the IOU to select between the primary
and alternate character sets and are sent to the character
generator on lines RA9 and RA1 o.

The data for each row of characters are read eight times, once
for each of the eight lines of dots making up the row of
characters. The data bits are sent to the character generator
along with VA, VB, and VC, the low-order bits from the vertical
counter. For each character being displayed, the character
generator puts out one of eight stored bit patterns selected by
the three-bit number made up of VA, VB, and vc.

Hardware Implementation

Figure 7-12 Video Timing Signals

The bit patterns from the character generator are loaded into the
74166 parallel-to-serial shift register and output as a serial bit
stream that goes to the video output circuit. The shift register is
controlled by signals named LDPS' (for load parallel-to-serial
shifter) and VID7M (for video 7 Mhz). In 40-column mode, LDPS'
strobes the output of the character generator into the shift
register once each microsecond, and VID7M shifts the bits out at 7
MHz.

The addressing for the 80-column display is exactly the same as
for the 40-column display: the 40 columns of display memory on
the 80-column card are addressed in parallel with the 40 columns
in main memory. The data from these two memories reach the
video data bus (lines VID0-VID7) via separate 74LS374 three-state
buffers. These buffers are loaded simultaneously, but their
outputs are sent to the character generator alternately by 0o and
01. In 80-column mode, LDPS' loads data from the character
generator into the shift register twice during each microsecond,
once during <f>o and once during 01, and VID7M runs at 14 MHz to
shift the data bits out twice as fast.

14M

riRjinjwLnjirLrinn^^

7M —
*0 —

DATA BUS

video phase

cpu phase

>^z<

VIDEO BUFFER X

LDPS' (40-column mode)

VIDEO BUS (40-column mode)
SHIFT REGISTER (40-column mode)
VID7M (40-column mode)

i_r

_Ti_ri_rTJi_rLrLrLn

The Video Display

159

Low-Resolution Display

In the graphics modes, va and vb are not used by the character
generator, so the IOU uses lines SEGA and segb to transmit HO and
HIRES', as shown in Table 7-13.

Table 7-13 Character-generator Display mode SEGA SEGB SEGC

Control Signals

Text VA VB VC

Graphics HO HIRES' VC

The low-resolution graphics display uses vc to divide the eight
display lines corresponding to a row of characters into two
groups of four lines each. Each row of data bytes is addressed
eight times, the same as in text mode, but each byte is
interpreted as two nybbles. Each nybble selects one of sixteen
colors. During the upper four of the eight display lines, VC is low
and the low-order nybble determines the color. During the lower
four display lines, vc is high and the high-order nybble
determines the color.

The bit patterns that produce the low-resolution colors are read
from the character-generator ROM in the same way the bit
patterns for characters are produced in text mode. The 74166
parallel-to-serial shift register converts the bit patterns to a serial
bit stream for the video circuits.

The video signal generated by the Apple Me includes a short
burst of 3.58 MHz signal that is used by an NTSC color monitor
or color TV set to generate a reference 3.58 MHz color signal.
The Apple lie's video signal produces color by interacting with
this 3.58 MHz signal inside the monitor or TV set. Different bit
patterns produce different colors by changing the duty cycles and
delays of the bit stream relative to the 3.58 MHz color signal. To
produce the small delays required for so many different colors,
the shift register runs at 14 MHz and shifts out 14 bits during
each cycle of the 1-MHz data clock. To generate a stream of
fourteen bits from each eight-bit pattern read from the ROM, the
output of the shift register is connected back to the register's
serial input to repeat the same eight bits; the last two bits are
ignored the second time around.

160 Hardware Implementation

Each bit pattern is output for the same amount of time as a
character: 1 .02 microseconds. Because that is exactly enough
time for three and a half cycles of the 3.58 MHz color signal, the
phase relationship between the bit patterns and the signal
changes by a half cycle for each successive pattern. To
compensate for this, the character generator puts out one of two
different bit patterns for each nybble, depending on the state of
HO, the low-order bit of the horizontal counter.

High-Resolution Display

The high-resolution graphics pages begin at memory locations
* 2 o o o and * 40 o o (decimal 8192 and 1 6384). These page addresses
are selected by address bits A1 3 and A1 4. In high-resolution mode,
these address bits are controlled by PG2 and 80VID, the signals
controlled by the display-page (PAGE2) and 80-column-video
(80COL) soft switches. As in text mode, 80VID inhibits addressing of
the second page because there is only one page of 80-column
text available for mixed mode.

In high-resolution graphics mode, the display data are still stored
in blocks like the one shown in Figure 7-11, but there are eight
of these blocks. As Table 7-1 1 and Table 7-12 show, vertical
counts va, vb, and vc are used for address bits A1 o, A1 1 , and A1 2,
which address eight blocks of 1024 bytes each. Remember that
in the display va, vb, and vc count adjacent horizontal lines in
groups of eight. This addressing scheme maps each of those
lines into a different 1024-byte block. It might help to think of it
as a kind of eight-way multiplexer: it's as if eight text displays
were combined to produce a single high-resolution display, with
each text display providing one line of dots in turn, instead of a
row of characters.

The high-resolution bit patterns are produced by the character-
generator ROM. In this mode, the bit patterns simply reproduce
the eight bits of display data. The low-order six bits of data reach
the ROM via the video data bus VID0-VID5. The IOU sends the
other two data bits to the ROM via RA9 and RA1 o.

— !§

The high-resolution colors described in Chapter 2 are produced
by the interaction between the video signal the bit patterns
generate and the 3.58 MHz color signal generated inside the
monitor or TV set. The high-resolution bit patterns are always
shifted out at 7 MHz, so each dot corresponds to a half-cycle of
the 3.58 MHz color signal. Any part of the video signal that

The Video Display

161

produces a single white dot between two black dots, or vice-
versa, is effectively a short burst of 3.58 MHz and is therefore
displayed as color. In other words, a bit pattern consisting of
alternating ones and zeros gets displayed as a line of color. The
high-resolution graphics subroutines produce the appropriate bit
patterns by masking the data bits with alternating ones and
zeros.

To produce different colors, the bit patterns must have different
phase relationships to the 3.58 MHz color signal. If alternating
ones and zeros produce a certain color, say green, then
reversing the pattern to zeros and ones will produce the
complementary color, purple. As in the low-resolution mode, each
bit pattern corresponds to three and a half cycles of the color
signal, so the phase relationship between the data bits and the
color signal changes by a half cycle for each successive byte of
data. Here, however, the bit patterns produced by the hardware
are the same for adjacent bytes; the color compensation is
performed by the high-resolution software, which uses different
color masks for data being displayed in even and odd columns.

To produce other colors, bit patterns must have other timing
relationships to the 3.58 MHz color signal. In high-resolution
mode, the Apple Me produces two more colors by delaying the
output of the shift register by half a dot (70 ns), depending on
the high-order bit of the data byte being displayed. (The high-
order bit doesn't actually get displayed as a dot, because at
7 MHz there is only time to shift out seven of the eight bits.)

As each byte of data is sent from the character generator to the
shift register, high-order data bit D7 is also sent to the PAL. If D7
is off, the PAL transmits shift-register timing signals LDPS' and
v I D7M normally. If D7 is on, the PAL delays LDPS ' and v I D7M by 70
nanoseconds, the time corresponding to half a dot. The bit
pattern that formerly produced green now produces orange; the
pattern for purple now produces blue.

A note about timing: For 80-column text, the shift register is clocked
at twice normal speed. When 80-column text is used with graphics
in mixed mode, the PAL controls shift-register timing signals LDPS'
and VID7M so that the graphics portion of the display works correctly
even when the text window is in 80-column mode.

162 Hardware Implementation

Video Output Signals

The stream of video data generated by the display circuits
described above goes to a linear summing circuit built around
transistor Q1 where it is mixed with the sync signals and the
color burst. Resistors R3, R5, R7, R10, R13, and R15 adjust the
signals to the proper amplitudes, and a tank circuit (L3 and C32)
resonant at 3.58 MHz conditions the color burst.

The resulting video signal is an NTSC-compatible composite-
video signal that can be displayed on a standard video monitor.
The signal is similar to the EIA (Electronic Industries Association)
standard positive composite video (see Table 7-14). This signal is
available in two places in the Apple Me:

• At the phono jack on the back of the Apple He. The sleeve of
this jack is connected to ground and the tip is connected to
the video output through a resistor network that attenuates it
to about 1 volt and matches its impedance to 75 ohms.

• At the internal video connector on the Apple He circuit board
near the RCA jack, J13 in Figure 7-1 4c. It is made up of four
Molex-type pins, 0.25 inches tall, on 0.10 inch centers. This
connector carries the video signal, ground, and two power
supplies, as shown in Table 7-14.

Table 7-14 Internal Video Connector

Signals

Pin Number

Name

Description

GROUND System common ground

VIDEO NTSC-compatible positive composite video. White

level is about 2.0 volts, black level is about 0.75
volts, and sync level is 0.0 volts. This output is not
protected against short circuits.

-5V -5 volt power supply

+ 1 2V +12 volt power supply

The Video Display

163

Built-in HO Circuits

The use of the Apple lie's built-in I/O features is described in
Chapter 2. This section describes the hardware implementation of
all of those features except the video display described in the
previous sections. The IOU (Input/Output Unit) generates the
output signals for the speaker, the cassette interface, and the
annunciators directly. The other I/O features are handled by
smaller ICs, as described below.

The addresses of the built-in I/O features are described in
Chapter 2 and listed in Table 2-2, Table 2-11, and Table 2-12. All
of the built-in I/O features except the displays use memory
locations between *cooo and $C070 (decimal 49152 and 49264).
The I/O address decoding is performed by three ICs: a 74LS138,
a 74LS154, and a 74LS251.

The 74LS138 decodes address lines A8, A9, A1 o, and A1 1 to select
address pages on 256-byte boundaries starting at *C000 (decimal
49152). When it detects addresses between *cooo and $coff, it
enables the IOU and the 74LS154. The 74LS154 in turn decodes
address lines A4, A5, A6, and A7 to select 16-byte address areas
between *cooo and $coff. Addresses between *C060 and $C06F
enable the 74LS251 that multiplexes the hand control switches
and paddles; addresses between $C070 and *C07F reset the
NE558 quadruple timer that interfaces to the hand controls, as
described below in the section "Game I/O Signals".

The Keyboard

The Apple lie's keyboard is a matrix of keyswitches connected to
an AY-3600-type keyboard decoder via a ribbon cable and a 26-
pin connector. The AY-3600 scans the array of keys over and
over to detect any keys pressed. The scanning rate is set by the
external resistor-capacitor network made up of C70 and R32. The
debounce time is also set externally, by C71 .

The AY-3600's outputs include five bits of key code plus
separate lines for i control | , | shift l ,anv-kev-down, and key board
strobe. The any-key-down and keyboard-strobe lines are
connected to the IOU, which addresses them as soft sw itches.
The key-code lines, along with [ control | and I shift | , are inputs
to a separate 2316 ROM. The ROM translates them to the
character codes that are enabled onto the data bus by signals
named KBD' and enkbd' . The KBD' signal is enabled by the MMU
whenever a program reads location *C000, as described in
Chapter 2.

164 Hardware Implementation

■

■M

I
I

Table 7-15 Keyboard Connector
Signals

Pin Number

Name

Description

1,2,4,
6,8, 10,
23, 25,
12, 22

Y0-Y9

Y-direction key-matrix connections

•5

+5 volt supply

5, 7, 9, 15

n. c.

LCNTL

Line from | CONTROL | key

GND

System common ground

14, 16,
20, 21, 19,
26, 17

X0-X7

LSHFT'

X-direction key-matrix connections

Line from SHIHT| key

Connecting a Keypad

There is a smaller connector wired in parallel with the keyboard
connector. You can connect a ten-key numeric pad to the
Apple He via this connector.

Table 7-16 Keypad Connector Signals Pin Number

Name

Description

1,2,5,
3, 4,6

Y0-Y5
n. c.

Y-direction key-matrix connections

9, 11,

10, 8

X4-X7

X-direction key-matrix connections

Built-in I/O Circuits

165

Table 7-17 Speaker Connector
Signals

Cassette 110

The two miniature phone jacks on the back of the Apple lie are
used to connect an audio cassette recorder for saving programs.
The output signal to the cassette recorder comes from a pin on
the IOU via resistor network R6 and R9, which attenuates the
signal to a level appropriate for the recorder's microphone input.
Input from the recorder is amplified and conditioned by a type
741 operational amplifier and sent to one of the inputs of the
74LS251 input multiplexer.

The signal specifications for cassette I/O are:

Input: 1 volt (nominal) from recorder Earphone or Monitor
output. Input impedance is 12K ohms.

Output: 25 millivolts to recorder Microphone input. Output
impedance is 100 ohms.

The Speaker

The Apple lie's built-in loudspeaker is controlled by a single bit of
output from the IOU (Input Output Unit). The signal from the IOU
is AC coupled to Q5, an MPSA13 Darlington transistor amplifier.
The speaker connector is a Molex KK100 connector, J18 in
Figure 7-1 4b, with two square pins 0.25 inches tall and on 0.10-
inch centers.

A light-emitting diode is connected in parallel across the speaker
pins such that, when the speaker is not connected, the diode
glows whenever the speaker signal is on. This diode is used as
a diagnostic indicator during assembly and testing of the
Apple lie.

Pin Number Name

Description

SPKR

+ 5

Speaker signal. This line will deliver about 0.5
watts into an 8-ohm speaker.

+5V power supply. Note that the speaker is not
connected to system ground.

166

Hardware Implementation

Game //O Signals

Several I/O signals that are individually controlled via soft
switches are collectively referred to as the game signals. Even
though they are normally used for hand controls, these signals
can be used for other simple I/O applications. There are five
output signals: the four annunciators, numbered AO through A3,
and one strobe output. There are three one-bit inputs, called
switches and numbered swo through SW2, and four analog inputs,
called paddles and numbered pdlo through pdl.3.

The annunciator outputs are driven directly by the IOU (Input
Output Unit). These outputs can drive one TTL (transitor-transitor
logic) load each; for heavier loads, you must use a transistor or a
TTL buffer on these outputs. These signals are only available on
the 16-pin internal connector (see Table 7-18).

The strobe output is a pulse transmitted any time a program
reads or writes to location $C040. The strobe pin is connected to
one output of the 74LS1 54 address decoder. This TTL signal is
normally high; it goes low during $0 of the instruction cycle that
addresses location *C040. This signal is only available on the 16-
pin internal connector (see Table 7-18).

The game inputs are multiplexed along with the cassette input
signal by a 74LS251 eight-input multiplexer enabled by the C06X'
signal from the 74LS154 I/O address decoder. Depending on the
low-order address, the appropriate game input is connected to bit
7 of the data bus.

The switch inputs are standard low-power Shottky TTL inputs. To
use them, connect each one to 220-ohm pull-up resistors
connected to the +5-volt supply and through single-pole,
momentary-contact pushbutton switches to ground.

The hand-control inputs are connected to the timing inputs of an
NE558 quadruple 555-type analog timer. Addressing $C07X sends
a signal from the 74LS154 that resets all four timers and causes
their outputs to go to one (high). A variable resistance of up to
150K ohms connected between one of these inputs and the +5V
supply controls the charging time of one of four 0.022-microfarad
capacitors. When the voltage on the capacitor passes a certain
threshold, the output of the NE558 changes back to zero (low).

Built-in I/O Circuits

167

Programs can determine the setting of a variable resistor by
resetting the timers and then counting time until the selected
timer input changes from high to low. The resulting count is
proportional to the resistance.

The game I/O signals are all available on a 16-pin DIP socket
labelled GAME I/O on the main circuit board inside the case.
The switches and the paddles are also available on a D-type
miniature connector on the back of the Apple Me; see J8 and J15
in Figure 7-1 4d.

Table 7-18 Game I/O Connector
Signals

Internal-
Connector
Pin Number

Back-panel-
Connector
Pin Number

Signal
Name

Description

2,3,4

6, 10,7, 11

7,1,6

5, 8, 4, 9

15, 14, 13, 12

9, 16

+ 5V

PB0-PB2

STROBE'

PDL0-PDL3

OND
AN0-AN3

n. c.

+5 power supply. Total
current drain from this pin
must not exceed 100mA.

Switch inputs. These are
standard 74LS inputs.

Strobe output. This line goes
low during $0 ot a read or
write instruction to location
SC040.

Hand control inputs. Each of
these should be connected
to a 150K-ohm variable
resistor connected to +5V.

System ground.

Annunciators. These are
standard 74LS TTL outputs
and must be buffered to
drive other than TTL inputs.

Nothing is connected to
these pins.

168

Hardware Implementation

Expanding the Apple He

The main circuit board of the Apple He has eight empty card
connectors or slots on it. These slots make it possible to add
features to the Apple Me by plugging in peripheral cards with
additional hardware. Chapter 6 describes the standards for
programming peripheral cards for the Apple He. This section
describes the hardware that supports them, including all of the
signals available on the expansion slots.

The Expansion Slots

The seven connectors lined up across the back part of the
Apple lie's main circuit board are the expansion slots, also called
peripheral slots or simply slots, numbered from 1 to 7. They are
50-pin PC-card edge connectors with pins on 0.10-inch centers.
A PC card plugged into one of these connectors has access to
all of the signals necessary to perform input and output and to
execute programs in RAM or ROM on the card. These signals
are described briefly in Tables 7-1 9a, 7-1 9b, and 7-1 9c. The
following paragraphs describe the signals in general and mention
a few points that are often overlooked. For further details, refer
to the schematic diagram in Figures 7-1 4a, 7-1 4b, 7-1 4c, and 7-1 4d.

The Peripheral Address Bus

The 6502s address bus is buffered by two 74LS244 octal three-
state buffers. These buffers, along with a buffer in the 6502's
R/W line, are enabled by a signal derived from the DMA' daisy-
chain on the expansion slots. Pulling the peripheral line DMA' low
disables the address and R/W buffers so that peripheral DMA
circuitry can control the address bus. The DMA address and
R/W signals supplied by a accessory card must be stable all
during $o of the instruction cycle, as shown in Figure 7-13.

Another signal that can be used to disable normal operation of
the Apple lie is I NH ' . Pulling I NH ' low disables all of the memory
in the Apple lie except the part in the I/O space from *C000 to
$CFFF. A peripheral card that uses either INH' or DMA' must
observe proper timing; in order to disable RAM and ROM cleanly,
the disabling signal must be stable all during <f>o of the instruction
cycle (refer to the timing diagram in Figure 7-13).

The peripheral devices should use I/O select' and
DEVICE SELECT' as enables. Most peripheral ICs require their

Expanding the Apple lie

169

enable signals to be present for a certain length of time before
data is strobed into or out of the device. Remember that I/O
SELECT' and DEVICE select' are only asserted during </>o high.

The Peripheral Data Bus ^

The Apple lie has two versions of the 6502 data bus: an internal
bus, MD0-MD7, connected directly to the 6502; and an external bus,
D0-D7, driven by a 74LS245 octal bidirectional bus buffer. The
6502 is fabricated with MOS circuitry, so it can drive capacitive
loads of up to about 130 pF. If peripheral cards are installed in
all seven slots, the loading on the data bus can be as high as
500 pF, so the 74LS245 drives the data bus for the peripheral
cards. The same argument applies if you use MOS devices on
peripheral cards: they don't have enough drive for the fully-
loaded bus, so you should add buffers.

Loading and Driving Rules

Tables 7-1 9a, 7-1 9b, and 7-1 9c show the drive requirements and
loading limits for each pin on the expansion slots. The address
bus, the data bus, and the R/W line should be driven by three-
state buffers. Remember that there is considerable distributed
capacitance on these busses and that you should plan on
tolerating the added load of up to six additional peripheral cards.
MOS devices such as PIAs and ACIAs cannot switch such heavy
capacitive loads. Connecting such devices directly to the bus will
lead to possible timing and level errors.

Interrupt and DMA Daisy Chains

The interrupt requests (IRQ' and NMI ') and the direct-memory
access (DMA ' ) signal are available at all seven expansion slots. A
peripheral card requests an interrupt or a DMA transfer by pulling
the appropriate output line low (active). If two peripheral cards
request an interrupt or a DMA transfer at the same time, they will
contend for the data and address busses. To prevent this, two
pairs of pins on each connector are wired as a priority daisy
chain. The daisy-chain pins for interrupts are INT IN and INT OUT,
and the pins for DMA are DMA IN and DMA OUT, as shown for J1-J7 in
Figure 7-1 4d.

Each daisy chain works like this: the output from each connector
goes to the input of the next higher numbered one. For these
signals to be useful for cards in lower numbered connectors, all
of the higher numbered connectors must have cards in them, and
all of those cards must connect DMA IN to DMA OUT and INT IN to I NT
OUT. Whenever an accessory card uses pin DMA' , it must do so

170 Hardware Implementation

only if its DMA IN line is active, and it must disable its DMA OUT line
while it is using DMA'. The INT IN and INT OUT lines must be used
the same way: enable the card's interrupt circuits with IN"I IN, and
disable INT out whenever IRQ' or nmi ' is being used.

Figure 7-1 3 Peripheral-signal Timing

ADDRESS w^

A0-A15, R/w-> X
INH', DMA' {

PERIPHERAL SELECT
I/O SELECT' )
DEVICE SELECT [■
I/O STROBE' \

Y+- 1 1 ns (max) 1 5 ns (min) ■

Expanding the Apple He

171

Table 7-1 9a Expansion Slot Signals
•Loading limits are for each card.

Pin Number

Name

Description

I/O SELECT Normally high; goes low during $0 when the 6502
addresses location $CnXX, where n is the
connector number. This line can drive 10 LS TTL
loads.*

2-17

A0-A15

R/W

SYNC

I/O
STROBE'

RDY

DMA'

INT OUT

DMA OUT

+ 5V

GND

Three-state address bus. The address becomes
valid during $1 and remains valid during <f>0. Each
address line can drive 5 LS TTL loads.*

Three-state read/write line. Valid at the same time
as the address bus; high during a read cycle, low
during a write cycle. It can drive 2 LS TTL loads.*

Composite horizontal and vertical sync, on
expansion slot 7 ONLY. This line can drive 2 LS
TTL loads.*

Normally high; goes low during $0 when the 6502
addresses a location between $C800 and
$CFFF. This line can drive 4 LS TTL loads.

Input to the 6502. Pulling this line low during <f>1
halts the 6502 with the address bus holding the
address of the location currently being fetched.
This line has a 3300 ohm pullup resistor to +5V.

Input to the address bus buffers. Pulling this line
low during <f>1 disconnects the 6502 from the
address bus. This line has a 3300 ohm pullup
resistor to +5V

Interrupt priority daisy-chain output. Usually

connected to pin 28 (INT IN).

(Note: on slot 7 ONLY, this pin can be connected

to the graphics-mode signal GR: see text for

details.)

DMA priority daisy-chain output. Usually
connected to pin 22 (DMA I N).

+5-volt power supply. A total of 500mA is
available for all accessory cards.

System common ground.

172

Hardware Implementation

Table 7-1 9b Expansion Slot Signals, Pin Number

continued

Name

Description

•Loading limits are tor each card.

31
32

33
34
35
36
37
38

DMA IN

INT IN

NMI'

IRQ'

RES'
INH'

-12V

-SV

3.58M

DMA priority daisy-chain input. Usually connected
to pin 24 (DMA OUT).

Interrupt priority daisy-chain input. Usually
connected to pin 23 ( I NT OUT ).

Non-maskable interrupt to 6502. Pulling this line
low starts an interrupt cycle with the
interrupt-handling routine at location $03FB. This
line has a 3300 ohm pullup resistor to +5V.

Interrupt request to 6502. Pulling this line low
starts an interrupt cycle only if the
interrupt-disable (I) flag in the 6502 is not set.
Uses the interrupt-handling routine at location
J03FE. This line has a 3300 ohm pullup resistor
to +5V.

Pulling this line low initiates a reset routine, as
described in Chapter 4.

Pulling this line low during $1 inhibits (disables)
the memory on the main circuit board. This line
has a 3300 ohm pullup resistor to +5V.

-12 volt power supply. A total of 200mA is
available for all accessory cards.

-5 volt power supply. A total of 200mA is
available for all accessory cards.

3.58 MHz color reference signal, on slot 7 only.
This line can drive 2 LS TTL loads.*

System 7 MHz clock. This line can drive 2 LS TTL
loads.*

System 2 MHz asymmetrical clock. This line can
drive 2 LS TTL loads.*

6502 phase 1 clock. This line can drive 2 LS TTL
loads.*

Expanding the Apple He

173

Table 7-1 9c Expansion Slot Signals,
continued

'Loading limits are for each card.

Pin Number

Name

Description

42-49

juPSYNC

</>0

DEVICE
SELECT'

D0-D7

-12V

The 6502 signals an operand fetch by driving this
line high during the first read cycle of each
instruction.

6502 phase clock. This line can drive 2 LS TTL
loads.*

Normally high; goes low during $0 when the 6502
addresses location $C0nX, where n is the
connector number plus 8. This line can drive 10
LS TTL loads.*

Three-state buffered bi-directional data bus. Data
becomes valid during 4>0 high and remains valid
until 4>0 goes low. Each data line can drive one LS
TTL load.*

+ 12 volt power supply. A total of 250mA is
available for all accessory cards.

Video Signals on Slot 7

The video signals are available only on the auxiliary slot and not
on the numbered expansion slots, except for slot 7. The video
signals available on expansion slot 7 are SYNC, the composite
horizontal and video sync signal, on pin 19, and 3.58M, the color
reference signal, on pin 35. Early production Apple lies, identified
by a circuit board part number ending in -A, do not have this
feature.

The signal that enables the graphics modes, named gr, is not
normally available on the numbered expansion slots. You can make
it available on pin 23 of slot 7 by completing the circuit at location
X7 on the main circuit board. Remember to turn off the power
before changing anything inside the Apple lie. Also remember that
changes such as this are at your own risk and may void the
warranty.

The Auxiliary Slot

The large connector at the left side of the Apple He's main circuit
board is the auxiliary slot. It is a 60-pin PC-card edge connector
with pins on 0.10-inch centers. A PC card plugged into this
connector has access to all of the signals used in producing
the video display. These signals are described briefly in Tables

174

Hardware Implementation

7-20a, 7-20b, and 7-20c. For further details, refer to the
schematic diagram in Figures 7-1 4a, 7-1 4b, 7-1 4c, and 7-1 4d.

Many of the internal signals that are not available on the
expansion slots are on the auxiliary slot. By using both kinds of
connectors, manufacturing and repair personnel can gain access
to most of the signals needed for diagnosing problems in the
Apple lie.

80-column Display Signals

The additional memory needed for producing an 80-column text
display is on the 80-column text card, along with the buffers that
transfer the data to the video data bus, as described above in
the section "Text Displays". The signals that control the 80-
column text data include the system clocks 4>o and <£1, the
multiplexed RAM address RA0-RA7, the RAM address-strobe
signals PR AS' and PC as', and the auxiliary-RAM enable signals,
EN80' and R/W80. The EN80' enable signal is controlled by the
80STORE soft switch described in Chapter 4. Data is sent to the
auxiliary memory via the internal data bus MD0-MD7; the data is
transferred to the video generator via the video data bus VIDO-
VID7.

Expanding the Apple Me

175

Table 7-20a Auxiliary Slot Signals

Pin Number Name

Description

3 . 58M 3.58 MHz video color reference signal. This line

can drive two LS TTL loads.

V I D7M Clocks the video dots out of the 741 66

parallel-to-serial shift register. This line can drive
two LS TTL loads.

SYNC Video horizontal and vertical sync signal. This line

can drive two LS TTL loads.

PR AS' Multiplexed RAM row-address strobe. This line

can drive two LS TTL loads.

Third low-order vertical-counter bit. This line can
drive two LS TTL loads.

C07X' Hand-control reset signal. This line can drive two

LS TTL loads.

WNDW Video non-blank window. This line can drive two

LS TTL loads.

SEGA First low-order vertical counter bit. This line can

drive two LS TTL loads.

51, 10, 49,
48, 13, 14,
46,9

RA0-RA7 Multiplexed RAM-address bus. This line can drive
two LS TTL loads.

11, 12

RDMEN1, Enable signals for the ROMs on the main circuit

RDMEN2 board.

R/W Read/write signal from 6502. This line can drive

two LS TTL loads.

44, 43, 40,
39,21,20,
17, 16

MDO -MD7 Internal (unbuffered) data bus. This line can drive
two LS TTL loads.

176

Hardware Implementation

Table 7-20b Auxiliary Slot Signals,

Pin Number

continued

45,42,41,
38,22, 19,
18, 15

Name

Description

VID0-VID7 Video data bus. This three-state bus carries video
data to the character generator.

4>0 6502 clock phase 0. This line can drive two LS

TTL loads.

CLRGAT ' Color-burst gating signal. This line can drive two
LS TTL loads.

80 V I D ' Enables 80-column display timing. This line can

drive two LS TTL loads.

EN80 ' Enable for auxiliary RAM. This line can drive two

LS TTL loads.

ALTVID' Alternative video output to the video summing
amplifier.

SEROUT ' Video serial output from 74166 parallel-to-serial
shift register.

ENVID' Normally low; driving this line high disables the

character generator such that the video dots from
the shift register are all high (white), and
alternative video can be sent out via ALTVID'.
This line has a 1000 ohm pulldown resistor to
ground.

+ 5

GND

+5 volt power supply.

System common ground.

14.3 MHz master clock signal. This line can drive
two LS TTL loads.

PCAS ' Multiplexed column-address strobe. This line can

drive two LS TTL loads.

LDPS ' Strobe to video parallel-to-serial shift register. This

signal goes low to load the contents of the video
data bus into the shift register. This line can drive
two LS TTL loads.

Expanding the Apple He

177

Table 7-20c Auxiliary Slot Signals,

continued

Pin Number

Name

Description

35 R/W80 Read/write signal for RAM on the 80-column text

card. This line can drive two LS TTL loads.

36 4>1 6502 clock phase 1 . This line can drive two LS

TTL loads.

37 CASEN' Column-address enable. This signal is disabled

(held high) during accesses to memory on the
auxiliary card. This line can drive two LS TTL
loads.

47 ho Low-order horizontal byte counter. This line can

drive two LS TTL loads.

50 AN3 Output of annunciator number 3. This line can

drive two LS TTL loads.

52 r/w 6502 read/write signal. This line can drive two LS

TTL loads.

53 Q3 2 MHz asymmetrical clock. This line can drive two

LS TTL loads.

54 SEGB Second low-order vertical-counter bit. This line

can drive two LS TTL loads.

55 ENFIRM Normally high; pulling this line low

disables R0M1 and R0M2 on the main circuit
board. This line has a 3300-ohm pullup resistor to
+ 5V.

56, 57 RA9', RA1 ' Character-generator control signals from the IOU.

This line can drive two LS TTL loads.

58 GR Graphics-mode enable signal. This line can drive

two LS TTL loads.

59 7M 7 MHz timing signal. This line can drive two LS

TTL loads.

60 ENTMG ' Normally low; pulling this line high disables the

master timing from the PAL. This line has a 1000
ohm pulldown resistor to ground.

178

Hardware Implementation

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Hardware Implementation

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182

Hardware Implementation

Appendices

185 Appendix A: The 6502 Instruction Set

197 Appendix B: Tables

217 Appendix C: Directory of Built-in Subroutines

225 Appendix D: Differences Between the Apple lie and Apple II Plus

231 Glossary

253 Bibliography

257 Index

266 Numbers

266 Cast of Characters

.,;

...

Appendices

183

e'i:.:J » ?

Appendix A

The 6502 Instruction Set

The Following Notation Applies to This
Summary:

Accumulator

X. Y

index Registers

Memory

Borrow

Processor Status Register

Stack Pointer

Change

No Change

Add

Logical AND

Subtract

Logical Exclusive Or

Transfer Frorr: Sr.tack

Transfer To Stack

Transfer To

—

Transfer To

Logical OR

Program Counter

PCH

Program Counter High

PCL

Program Counter Low

OPER

Operand

Immediate Addressing Mode

FIGURE 1 ASL-SHIFT LEFT ONE BIT OPERATION

7 6 5 4 3 2 10

FIGURE 2 ROTATE ONE BIT LEFT (MEMORY
OR ACCUMULATOR)

M OR A

FIGURE 3 ROTATE ONE BIT RIGHT (MEMORY
OR ACCUMULATOR)

L7=

7 6 5 4 3 2 1

NOTE 1: BIT — TEST BITS

Bit 6 and 7 are transferred to the status register. If the
result of A A M is zero then Z-1, otherwise Z=0

The 6502 Instruction Set

185

6502 Microprocessor Instructions

ADC

Add Memory to Accumulator with

LDA

Carry

LDX

AND

"AND ' Memory with Accumulator

LDY

ASL

Shift Lett One Bit (Memory or
Accumulator)

LSR

BCC

Branch on Carry Clear

NOP

BCS

Branch on Carry Set

ORA

BEO

Branch on Result Zero

PHA
PHP

BIT

Test Bits in Memory with

BMI

Accumulator

Branch on Result Minus

PLA

PLP

BNE

Branch on Result not Zero

BPL

Branch on Result Plus

ROL

BRK

Force Break

BVC

Branch on Overflow Clear

ROR

BVS
CLC

Branch on Overflow Set
Clear Carry Flag

RTI
RTS

CLD

Clear Decimal Mode

CLI

Clear Interrupt Disable Bit

SBC

CLV

Clear Overflow Flag

CMP

Compare Memory and Accumulator

SEC

CPX

Compare Memory and Index X

SED

CPY

Compare Memory and Index Y

SEI

DEC

Decrement Memory by One

STA

DEX

Decrement Index X by One

STX

DEY

Decrement Index Y by One

STY

EOR
INC

"Exclusive-Or" Memory with

Accumulator

Increment Memory by One

TAX
TAY
TSX
TXA

INX

Increment Index X by One

TXS
TYA

INY

increment Index Y by One

JMP

Jump to New Location

JSR

Jump to New Location Saving

Load Accumulator with Memory
Load Index X with Memory
Load Index Y with Memory
Shift Right one Bit (Memory or
Accumulator!

No Operation

"OR" Memory with Accumulator

Push Accumulator on Stack

Push Processor Status on Stack

Pull Accumulator from Stack

Pull Processor Status from Stack

Rotate One Bit Lett 'Memory or

Accumulator)

Rotate One Bit Right iMemory or

Accumulator!

Return from Interrupt

Return from Subroutine

Subtract Memory from Accumulator

with Borrow

Set Carry Flag

Set Decimal Mode

Set Interrupt Disable Status

Store Accumulator in Memory

Store Index X in Memory

Store Index Y in Memory

Transfer Accumulator to Index X
Transfer Accumulator to Index Y
Transfer Stack Pointer to Index X
Transfer Index X to Accumulator
Transfer Index X to Stack Pointer
Transfer Index Y to Accumulator

Return Address

— •-

186

The 6502 Instruction Set

Programming Model

ACCUMULATOR

INDEX REGISTER Y

INDEX REGISTER X

PCH

PCL

PROGRAM COUNTER

STACK POINTER

B D I Z C

PROCESSOR STATUS REGISTER. "P

CARRY
ZERO

INTERRUPT DISABLE
DECIMAL MODE
BREAK COMMAND
OVERFLOW
■ NEGATIVE

Programming Model

187

Instruction Codes

Assembly

HEX

Operation

Addressing

Language

No.

"P" Status Reg.

Description

Mode

Form

Code

Bytes

N ZC I D V

ADC

Add memory to

A-M-C — A.C

Immediate

ADC »Oper

n/vV — v/

accumulator with carry

Zero Paqe

ADC Oper

Zero Page.X

ADC Oper.X

Absolute

ADC Oper

Absolute. X

ADC Oper.X

Absolute, Y

ADC Oper.Y

(mdirect.XI

ADC (Oper.X)

(Indirect' Y

ADC (Oper).Y

AND

"AND" memory with

AAM —A

Immediate

AND nOper

accumulator

Zero Page

AND Oper

Zero Page.X

AND Oper.X

Absolute

AND Oper

Absolute. X

AND Oper.X

Absolute. Y

AND Oper.Y

(Indirect.X)

AND (Oper.X)

(Indirect), Y

AND (Oper).Y

ASL

Shitt left one bit

(See Figure 1)

Accumulator

ASL A

vW—

(Memory or Accumulator)

Zero Page

ASL Oper

Zero Page.X

ASL Oper.X

Absolute

ASL Oper

Absolute. X

ASL Oper.X

BCC

Branch on carry clear

Branch on 00

Relative

BCC Oper

BCS

Branch on carry set

Branch on 01

Relative

BCS Oper

BED

Branch on result zero

Branch on Z=1

Relative

BEO Oper

BIT

Test bits in memory

AAM. M 7 — N,

Zero Page

BIT 1 Oper

M 7 v' M 6

with accumulator

M 6 -»V

Absolute

BIT 1 Oper

BMI

Branch on result minus

Branch on N«1

Relative

BMI Oper

BNE

Branch on result not zero

Branch on Z=0

Relative

BNE Oper

BPL

Branch on result plus

Branch on N»0

Relative

BPL oper

BRK

Force Break

Forced
Interrupt
PC-2 ♦ P ♦

Implied

BRK 2

1 —

BVC

Branch on overflow clear

Branch on V=0

Relative

BVC Oper

i^^s4

|l^^

Note 1 : Bits 6 and 7 are transferred to the status register. If the result of A AND M is zero,

then Z = 1 ; otherwise Z = 0.

Note 2: A BRK command cannot be masked by setting I.

§2

188

The 6502 Instruction Set

■A

Nime
Description

Operation

Addressing
Mode

Assembly

LanguaQe

Form

HEX
OP
Code

Bytes

"P" Status Reg
N ZC I V

BVS

Branch on overflow set

Branch on V=l

Relative

BVS Oper

CLC

Clear carry flag

0— C

Implied

CLC

_ _

CLO

Clear decimal mode

— D

implied

CLD

-0

CLI

0—1

Implied

— o -

CLV

Clear overflow flag

o— v

Implied

CLV

CMP

Compare memory and
accumulator

A - M

Immediate
Zero Page
Zero Page. X
Absolute
Absolute X
Absolute Y
(Indirect X)
(Indirect). Y

CMP nOper
CMP Oper
CMP Oper.X
CMP Oper
CMP Oper.X
CMP Oper.Y
CMP (Oper.X)
CMP (Oper) Y

C9
C5
D5
CD
DD
D9
C1
D1

2
2
2
3
3
3
2
2

CPX

Compare memory and
index X

X - M

Immediate
Zero Page
Absolute

CPX "Oper
CPX Oper
CPX Oper

EO
E4
EC

2
2
3

v/vV—

CPY

Compare memory and
index Y

Y - M

Immediate
Zero Page
Absolute

CPY oOper
CPY Oper
CPY Oper

CO
C4
CC

2
2

vvV

DEC

Decrement memory
by one

M - 1 — M

Zero Page
Zero Page.X
Absolute
Absolute. X

DEC Oper
DEC Oper.X
DEC Oper
DEC Oper.X

C6
D6
CE
DE

2
2

3
3

DEX

Decrement index X

by one

X - 1 —X

Implied

DEX

DEY

Decrement index Y
oy one

Y - 1 — Y

Implied

DEY

Instruction Codes

189

Assembly

HEX

Operation

Addressing

Language

T Stilus Reg

Description

Mode

Form

Code

Bytes

NZCIDV

EOR

"Exclusive 0'' memory

AVM»A

Immediate

EOR sOper

VV —

with accumulator

Zero Page

EOR Oper

Zero Page X

EOR Oper.X

Absolute

EOR Oper

Absolute. X

EOR Oper.X

Absolute.Y

EOR Oper.Y

llndirect.X)

EOR (Oper.X)

(Indirect). Y

EOR (Oper).Y

INC

Increment memory

M • 1 — M

Zero Page

INC Oper

by one

Zero Page.X

INC Oper.X

Absolute

INC Oper

Absolute. X

INC Oper.X

INX

Increment index X by one

X - 1 —X

Implied

INX

INY

Increment index ¥ by one

Y - 1 — Y

Implied

INY

JMP

Jump to new location

(PC.1) — PCL

Absolute

JMP Opet

(PC. 2) — PCH

Indirect

JMP (Oper)

JSR

Jump to new location

PC*2»

Absolute

JSR Oper

saving return address

(PC-»1) — PCL
(PC* 2) ^PCH

LDA

Load accumulator

M— A

Immediate

LDA nOper

VV —

with memory

Zero Page

LDA Oper

Zero Page.X

LDA Oper.X

Absolute

LDA Oper

Absolute. X

LDA Oper.X

Absolute.Y

LDA Oper.Y

(Indirect. X)

LDA (Oper.X)

(Indirect).Y

LDA (Oper).Y

LDX

M— X

Immediate

LDX uOper

Zero Page

LDX Oper

Zero Page.Y

LDX Oper.Y

Absolute

LDX Oper

Absolute.Y

LDX Oper.Y

LDY

M-~Y

Immediate

LDY sOper

with memory

Zero Page

LDY Oper

Zero Page.X

LDY Oper.X

Absolute

LDY Oper

Absolute. X

LDY Oper.X

190

The 6502 Instruction Set

J
J

Nimi
Deicrlpllon

Operation

Addressing
Made

Assembly

Unguagi
Form

HEX
OP
Code

No
Bytes

"P" Stilus Reg.
NZCIOV

LSR

Shift right one bit
(memory or accumulator)

(See Figure 1)

Accumulator
Zero Page
Zero Page.X
Absolute
Absolute. X

LSR A
LSR Oper
LSR Oper.X
LSR Oper
LSR Oper.X

4A
46
56
4E
5E

1
2
2
3
3

OVV-—

NOP

No operation

No Operation

Implied

NOP

ORA

"OR" memory with
accumulator

AVM —A

Immediate
Zero Page
Zero Page.X
Absolute
Absolute. X
Absolute.Y
(Indirect. X)
(Indirect), Y

ORA nOper
ORA Oper
ORA Oper.X
ORA Oper
ORA Oper.X
ORA Oper.Y
ORA (Oper.X)
ORA (Operl.Y

09
05
15
00
1D
19
01
11

2
2
2
3
3
3
2
2

PHA

Push accumulator
on stack

Implied

PHA

PHP

Push processor status
on stack

P»

Implied

PHP

PLA

Pull accumulator
from stack

Implied

PLA

Vv/

PLP

Pull processor status
from stack

P»

Implied

PLP

From Stack

ROL

Rotate one bit left
(memory or accumulator)

(See Figure 2)

Accumulator
Zero Page
Zero Page.X
Absolute
Absolute. X

ROL A
ROL Oper
ROL Oper.X
ROL Oper
ROL Oper.X

2A
26
36
2E
3E

1
2
2
3
3

VvV —

ROR

Rotate one bit right
(memory or accumulator)

(See Figure 3)

Accumulator
Zero Page
Zero Page.X
Absolute
Absolute. X

ROR A
ROR Oper
ROR Oper.X
ROR Oper
ROR Oper.X

6A
66
76
6E
7E

1
2
2
3

vVV —

Instruction Codes

191

Name
Description

Operation

Addressing
Mode

Assembly

Language

Form

HEX
OP

Code

No.
Bytes

"P" Status Reg
NZCIOV

RTI

Return trom interrupt

PtPCt

Implied

RTI

From Stacx

RTS

Return trom subroutine

PCf PC-1 — PC

Implied

RTS

SBC

Subtract memory from
accumulator with borrow

A - M -C — A

Immediate
Zero Page
Zero Page.X
Absolute
Absolute X
Absolute. Y
(Indirect. X)
(Indirect). Y

SBC "Oper
SBC Oper
SBC Oper.X
SBC Oper
SBC Oper.X
SBC Oper.Y
SBC (Oper.X)
SBC (Oper).Y

E9
E5
F5
ED
FD
F9
E1
F1

2
2
2
3
3
3
2
?

vVV \

SEC

Set carry flag

1 — C

Implied

SEC

— i

SED

Set decimal mode

1 ~D

Implied

SED

SEI

Set interrupt disable
status

1 —I

Implied

SEI

1 —

STA

Store accumulator
in memory

A — M

Zero Page
Zero Page.X
Absolute
Absolute. X
Absolute. Y
(Indirect. X)
(indirect). Y

STA Oper
STA Oper.X
STA Oper
STA Oper.X
STA Oper.Y
STA (Oper.X)
STA (Oper).Y

85
95
8D

9D
99

2
2
3
3
3
2
2

STX

Store index X in memory

X — M

Zero Page
Zero Page.Y

Absolute

STX Oper
STX Oper.Y
STX Oper

86
96

8F.

2
2
3

STY

Store index Y in memory

Y -»M

Zero Page
Zero Page.X
Absolute

STY Oper
STY Oper.X
STY Oper

84
94

2
2

TAX

Transfer accumulator
to index X

A -~X

Implied

TAX

TAY

Transfer accumulator
to index Y

A — Y

Implied

TAY

TSX

Transfer stack potnter
to tndex X

S ~X

Implied

TSX

192

The 6502 Instruction Set

Nimi

Description

Operation

Addressing
Mode

Assembly

Language

Form

HEX
OP
Code

No
Bytes

"P" Status Reg.
NZCIO V

TXA

Transfer index X
lo accumulator

X — A

Implied

TXA

TXS

Transfer index X to

stack pointer

x — s

Implied

TXS

TYA

Transfer index Y
to accumulator

Y ~A

Implied

TYA

Instruction Codes

193

Hex Operation Codes

00 -

BRK

2F -

5E -

LSR -

- Absolute. X

01 -

ORA -

(Indirect. Xi

30 -

BMI

5F -

02 -

31 -

AND —

'Indirect!, Y

60 -

RTS

03 -

32 -

61 —

ADC -

- Indirect. Xl

04 —

33 -

62 -

05 —

ORA -

Zero Page

34 -

63 —

06 —

ASL —

Zero Page

35 -

AND —

Zero Page. X

64 -

07 -

36 -

ROL -

Zero Page. X

65 -

ADC

- Zero Page

08 -

PHP

37 —

66 —

ROR

— Zero Page

09 —

ORA -

- Immediate

38 —

SEC

67 —

0A —

ASL —

Accumulator

39 -

AND —

Absolute. Y

68 —

PLA

OB -

3A -

69 -

ADC

— Immediate

OC -

3B -

6A -

ROR

— Accumulator

OD —

ORA -

- Absolute

3C -

6B -

OE —

ASL -

Absolute

3D -

AND -

Absolute. X

6C -

JMP -

- Indirect

OF -

3E -

ROL -

Absolute. X

6D -

ADC

— Absolute

10 —

BPL

3F —

6E -

ROR

— Absolute

11 —

ORA -

- (Indirect!. Y

40 —

RTI

6F —

12 —

41 —

EOR -

(Indirect. XI

70 -

BVS

13 —

42 —

71 —

ADC

— (Indirect!. Y

14 —

43 —

72 -

15 —

ORA -

- Zero Page. X

44 —

73 -

16 —

ASL -

Zero Page, X

45 —

EOR -

Zero Page

74 —

17 —

46 -

LSR -

Zero Page

75 —

ADC

— Zero Page. X

18 —

CLC

47 —

76-

ROR

— Zero Page. X

19 —

ORA -

- Absolute. Y

48 —

PHA

77 —

1A -

49 —

EOR -

Immediate

78 —

SEI

IB -

4A -

LSR —

Accumulator

79 -

ADC

— Absolute. Y

1C -

4B -

7A -

1D -

ORA -

- Absolute. X

4C -

JMP -

Absolute

7B -

1E -

ASL -

- Absolute. X

4D -

EOR -

- Absolute

7C -

IF -

4E -

LSR -

Absolute

7D -

ADC

— Absolute. X

20-

JSR

4F -

7E -

ROR

— Absolute. X

21 -

AND -

- (Indirect. XI

50 —

BVC

7F -

22 -

51 —

EOR (Indirect). Y

80 —

23-

52 —

81 -

STA

- (Indirect. X)

24 -

BIT -

Zero Page

53 -

82 —

25 -

AND

— Zero Page

54 -

83 —

26 -

ROL -

- Zero Page

55 -

EOR -

- Zero Page, X

84 -

-STY

— Zero Page

27 -

56-

LSR -

■ Zero Page. X

85 -

STA

— Zero Page

28 -

■ PLP

57 -

86-

STX

— Zero Page

29-

AND

— Immediate

58 -

CLI

87 -

2A -

- ROL

— Accumulator

59 -

EOR -

- Absolute. Y

88 -

DEY

2B -

5A -

89 -

2C -

- BIT -

- Absolute

5B -

8A -

- TXA

2D -

- AND

— Absolute

SC -

8B -

2E -

- ROL

— Absolute

5D -

- EOR -

- Absolute. X

BC-

- STY

— Absolute

The 6502 Instruction Set

8D -

STA -

Absolute

B4 -

LDY -

Zero Page X

8E -

STX -

Absolute

B5 -

LDA -

Zero Page X

8F -

B6 -

LDX —

Zero Page Y

DD -

CMP -

- Absolute X

90 -

BCC

B7 -

DE -

DEC -

- Absolute X

91 -

STA -

'Indirect'. Y

B8 -

CLV

DF -

92 -

B9 --

LDA -

Absolute Y

E0 -

CPX -

- Immediate

93 -

BA -

TSX

E1 -

SBC -

- 'Indirect X

94 -

STY -

Zero Page X

BB -

E2 -

95 -

STA -

Zero Page X

BC -

■ LDY -

Absolute X

E3 -

96 -

STX -

Zero Page. Y

BD -

LDA -

Absolute X

E4 -

CPX -

- Zero Page

97 -

BE -

LDX -

Absolute. Y

E5 -

SBC -

- Zero Page

98 -

TYA

BF -

E6 -

NC -

Zero Page

99 -

STA -

Absolute, Y

CO -

CPY -

Immediate

E7 -

9A -

TXS

C1 -

CMP -

- .Indirect. X

E8 -

INX

9B -

C2 -

E9 -

SBC -

- Immediate

9C -

C3 -

EA -

NOP

9D -

STA -

Absoruie x

C4 -

CPY -

Zero Page

9E -

C5 -

CMP -

- Zero Page

EC -

CPX -

- Absolute

9F -

C6 -

DEC -

- Zero Page

ED -

SBC -

- Absolute

A0 -

LDY -

immediate

C7 -

EE -

INC -

Absolute

A1 —

LDA -

Indirect X

C8 -

INY

EF -

A2 -

LDX -

Immediate

C9 -

CMP -

- Immediate

F0 -

BEO

A3 -

CA -

-DEX

F1 —

SBC -

- 'Indirect'. Y

A4 —

LDY -

Zeio Page

CB -

F2 -

AS -

LDA -

Zero Page

CC -

-CPY -

Absolute

F3 —

A6 -

LDX -

Zero Page

CD -

-CMP -

- Absolute

F4 -

A7 —

CE -

DEC -

- Absolute

F5 -

SBC -

- Zero Page. X

A8 —

TAY

CF -

F6 —

INC -

- Zero Page. X

A9 -

LDA -

immediate

DO -

BNE

F7 —

AA -

TAX

D1 -

CMP -

- (Indirect!. Y

F8 -

SED

AB -

D2 -

F9 -

SBC -

- Absolute Y

AC -

LDY -

Absolute

D3 -

FA -

AD -

■ Absolute

D4 -

FB -

AE -

LDX -

Absolute

D5 -

CMP -

- Zero Page, X

FC -

AF -

D6 -

DEC -

- Zero Page, X

FD -

SBC -

- Absolute. X

BO -

BCS

D7 -

FE -

INC -

- Absolute. X

B1 —

LDA -

(Indirect!. Y

D8 -

CLD

FF —

B2 -

D9 -

■ CMP -

- Absolute. Y

B3 -

DA -

Hex Operation Codes

195

II. J

11. J

% ^Y^ A '%'''■ W^M.'-iiY^M ;"■

■ j

II j

^' ' ■ i ; v:; "- f ■ - : .--.'V"3',; '-;:"- . = .,?-,-■■■ >-a|p

' * ■ *^

IIL -■

'- IS-' W> r '• : .'

K1H

• 11

■1 ■■

» ' ■' -" '.,■'".," ': ;

. . w np

( i," Vi' i! 'i' ' ■ >•" "'" " ''. "' .1!.'

Appendix a

Tables

This appendix contains copies of the tables you will need to refer
to a lot, for example, ASCII codes and soft-switch locations. The
figures all have their original figure numbers so you can refer to
the relevant sections in the text.

Table 2-2 Keyboard Memory
Locations

Location
Hex

Decimal

Description

*cooo

*C010

49152 -16384
49168 -16368

Keyboard data and strobe

Any-key-down flag and Clear-strobe switch

Tables

197

Table 2-3a Keys and ASCII Codes

Key

Normal

Control

Shift

Both

Codes are shown here in hexadecimal;

to find the decimal equivalents, use
Table 2-4.

DELETE

LEFT-ARROW

TAB

I DOWN -ARROW)
f UP -ARROW I

RETURN

RIGHT-ARROW

[ESCJ
space

. >

[{

2 A

198

Tables

Table 2-3b Keys and ASCII Codes,

continued

Codes are shown here in hexadecimal;
to find the decimal equivalents, use
Table 2-4.

Key

Normal

Control

Shift

Both

J!-

Tables

199

Table 2-4 The ASCII Character Set

Dec Hex Char

NUL

SOH

STX

ETX

EOT

ENQ

ACK

BEL

(

)

DLE

DC1

DC2

DC3

DC4

NAK

SYN

ETB

CAN

SUB

ESC

;

[

]

100

101

102

103

104

105

106

)

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

{

124

125

}

126

127

200

Tables

Table 2-6 The Display Character Sets

To identify particular characters and
values, refer to Table 2-4.

Hex Values

Primary Character Set:
Character Type Format

Alternate Character Set:
Character Type Format

$00-$1 F

Uppercase letters

Inverse

Uppercase letters

Inverse

$20-$3F

Special characters

Inverse

Special characters

Inverse

$40-$5F

Uppercase letters

Flashing

Uppercase letters

Inverse

$60-$7F

Special characters

Flashing

Lowercase letters

Inverse

$80-$9F

Uppercase letters

Normal

Uppercase letters

Normal

$AO-$BF

Special characters

Normal

Special characters

Normal

$C0-$DF

Uppercase letters

Normal

Uppercase letters

Normal

$EO-$FF

Lowercase letters

Normal

Lowercase letters

Normal

Table 2-7 Low-resolution Graphics
Colors

Colors may vary, depending upon the
controls on the monitor or television
set.

Nybble Value Color
Decimal Hex

Black

Brown

Magenta

Orange

Dark Blue

Grey 2

Purple

Pink

Dark Green

Light Green

Grey 1

Yellow

Medium Blue

Aquamarine

Light Blue

White

Table 2-8 High-resolution Graphics
Colors

Colors may vary, depending on the
adjustment of the monitor or television
set.

Bits 0-6

Bit 7 Off

Bit 7 On

Adjacent columns off

Black 1

Black 2

Even columns on

Purple

Blue

Odd columns on

Green

Orange

Adjacent columns on

White 1

White 2

Tables

201

Table 2-9 Video Display Page
Locations

Display mode

Page

Lowest
Address

Highest
Address

•Note: 80-column mode uses the
1024-byte page-1 locations in both
main and auxiliary memory. The
PAGE 2 switch is used to select one

40-column Text,

Low-resolution

Graphics

1
2

$400
$800

1024
2048

$7FF
$BFF

2047
3071

or the other for storing data (see the
section "Display Mode Switching").

80-column Text

$400

1024

$7FF

2047

High-resolution
Graphics

1
2

$2000
$4000

8192
18384

$3FFF
$5FFF

16383
24575

202

Tables

Table 2-10 Display Soft Switches

(1 ) This mode is only effective when
graphics-mode switch is ON.

(2) This switch has a different function
when the 80-column text card's
auxiliary text page is enabled for
writing. Refer to the next section,
"Addressing Display Pages Directly."

(3) This switch changes the function of
the PAGE2 switch for addressing the
auxiliary text memory on the extended
80-column text card. The next section
describes how to do this.

(4) Reading this location returns the
state of the vertical blanking
signal VBL . The function of VBL is
described in Chapter 7 in the section
"Video Output Signals."

Name

Function

Hex

Location
Decimal

Notes

ALTCHARSET

Alternate char, set on
Alternate char, set off
Read ALTCHARSET switch

*C00F 49167
*C00E 491GG
*C01E 49182

-16369 Write
-16370 Write
-16354 Read

TEXT Text mode on

Text mode off (graphics)
Read TEXT switch

*C051 49233 -16303
*C050 49232 -16304
*C01A 49178 -16358 Read

MIXED Mixed-mode on

Mixed-mode off
Read MIXED switch

*C053 49235 -16301 1
*C052 49234 -16302 1
*C01B 49179 -16357 Read

PAGE2 Page 2 on

Page 2 off (Page 1 )
Read PAGE 2 switch

*C055 49237 -16299 2
*C054 49236 -16300 2
*C01C 49180 -16356 Read

HIRES Hi-res mode on

Hi-res mode off
Read HIRES switch

*C057 49239 -16297 1
*C056 49238 -16298 1
*C01D 49181 -16355 Read

80CGL 80-column display on *C0 0D 49165 -16371 Write

80-column display off $C00C 49164 -16372 Write

Read 80COL switch $C01F 49183 -16353 Read

80STORE Store in auxiliary memory

Store in main memory
Read 80 STORE switch

*C001 49153 -16383 Write, 3
*C000 49152 -16384 Write, 3
*C018 49176 -16360 Read

VBL

Read vertical blanking

»C019 49177 -16359 Read, 4

Tables

203

Table 2-11 Annunciator Memory
Locations

No.

Annunciator
Pin*

State

Dec

Address
mal

Hex

*Pin numbers given are for the 16-pin
IC connector on the circuit board.

off
on

49240
49241

-16296
-16295

*C058
*C059

off
on

49242
49243

-16294
-16293

$C05A
$C05B

off
on

49244
49245

-16292
-16291

$C05C
*C05D

off
on

49246
49247

-16290
-16289

$C05E
$C05F

204

Tables

'■■■■ - --■— ■ ... .

Table 2-12 Secondary I/O Memory
Locations

For connector identification and pin
numbers, refer to Tables 7-1 7 and
7-18.

Address

Function

Decimal

Hex

Notes

Speaker

49200

- 1 6336

*C030

Read

Cassette Out

49184

-16352

$C020

Read

Cassette In

49248

- 1 6288

*C060

Read

Annunciator On

49241

-16295

$C059

Annunciator Off

49240

- 1 6296

*C0S8

Annunciator 1 On

49243

-16293

*C05B

Annunciator 1 Off

49242

-16294

*C05A

Annunciator 2 On

49245

-16291

$C05D

Annunciator 2 Off

49244

-16292

*C05C

Annunciator 3 On

49247

- 1 6289

*C05F

Annunciator 3 Off

49246

-16290

SC05E

Strobe Output

4921 e

-16320

*C040

Read

Switch Input

49249

-16287

*C061

Read

( | OPEN-APPLE key)

Switch Input 1

49250

- 1 6286

*C062

Read

(| SOL ID-APPLE | key)

Switch Input 2

49251

-16285

$C063

Read

Analog Input Reset

49264

-16272

$C070

Analog Input

49252

-16284

*C064

Read

Analog Input 1

49253

-16283

SC065

Read

Analog Input 2

49254

-16282

*C066

Read

Analog Input 3

49255

-16281

*C067

Read

Tables

205

Table 3-3a Control Characters with
C0UT1

(1 ) Only available when 80-column
firmware is active.

(2) Only works from the keyboard.

(3) Doesn't work from the keyboard.

Control ASCII Apple lie Action Taken by C0UT1

Character Name Name

Notes

CONTROLl - G (BEL) bell

CONTROL - H (BS) backspace

Produces a 1000 Hz tone for
0.1 second.

Moves cursor position one
space to the left; from left edge
of window, moves to right end
of line above.

CONTROL

CONTROL -

CONTROL

| C ONTROL j

| control]

CONTROL

(LF)

line feed

Moves cursor position down to
next line in window; scrolls if
needed.

(VT)

clear EOS

Clears from cursor position to 1
the end of the window.

(FF)

clear

Moves cursor position to upper 1
left corner of window and clears
window.

(CR)

return

Moves cursor position to left
end of next line in window;
scrolls if needed.

(SO)

normal

Sets display format normal. 1 , 3

(SI)

inverse

Sets display format inverse. 1 , 3

(DC1)

40-column

Sets display to 40-column. 1

(DC2)

80-column

Sets display to 80-column. 1

(DS3)

stop-list

Stops sending characters to the 1,2
display, until a key is pressed.

206

Tables

Table 3-3b Control Characters with
C0UT1 , continued

(1 ) Only available when 80-column
firmware is active.

(2) gotoXY is not supported under
BASIC: see the Apple Pascal
Operating System Reference Manual.

Control
Character

CONTROL

ASCII Apple Me
Name Name

Action Taken by C0UT1

Notes

CONTROL | - U (NAK) quit

CONTROL! - V (SYN) scroll

[CONTROL! - W (ETB) scroll-up

[CONTROL |- Y (EM) home

CONTROL |- Z (SUB) clear line

[CONTROL | - \ (FS) fwd. space

(GS) clear EOL

Deactivates 80-column 1

firmware, homes cursor,
and clears screen.

Scrolls the display down 1

one line, leaving the cursor
in the current position.

Scrolls the display up one 1
line, leaving the cursor in
the current position.

Moves cursor position to 1

upper left corner of window
(but doesn't clear).

Clears the line the cursor 1
position is on.

Moves cursor position one 1
space to the right; from
right edge of window,
moves it to left end of line
below.

Clears line from cursor 1

position to the right edge of
the window.

| CONTROL [ - A (RS) gotoXY

Using the next two
characters, minus 32, as
one-byte X and Y values,
moves the cursor position
toCH=X, CV=Y.

1,2

Table 3-4 Text Window

Memory

Locations

Window

Location

Minimum

Normal Values:

Maximum Values:

Parameter

Value:

40col.

80col.

40col. 80col.

Dec

Hex

Dec Hex

Dec

Hex

Dec

Hex

Dec

Hex Dec

Hex

Left Edge

$20

$27 79

$4F

Width

$21

$28

$50

$28 80

$50

Top Edge

$22

$17 23

$17

Bottom Edge

$23

1 $1

$18

$18 24

$18

Tables

207

Table 3-6 Escape Codes

(1 ) Old-style cursor-control key:
see text.

(2) Cursor-control key: see text.

(3) This code functions only when the
80-column firmware is active.

Escape Code

Function

Notes

Clears the window and homes the cursor

Moves the cursor up one line

Moves the cursor right one space

Moves the cursor left one space

Moves the cursor down one line

Clears to the end of the line

Clears to the bottom of the window

Moves the cursor up one line and turns on
escape mode

Moves the cursor left one space and turns on
escape mode

Moves the cursor right one space and turns on
escape mode

Moves the cursor down one line and turns on
escape mode

Turns on restricted-case mode

Turns off restricted-case mode

Switches to 40-column mode, homes the
cursor, and clears the screen

Switches to 80-column mode, homes the
cursor, and clears the screen

1 Deactivates the 80-column firmware

ESCj@

| ESC | A

[esc] b

[esc ) c

| ESC | D

| ESC | E

| ESC | F

| ESC | I

(Tscjt

| ESC | J

LjESCj —

| ESC | K

I ESC]—

| ESC | M

I ESC | +

| ESC | R

| ESC | T

| ESC | 4

| ESC | 8

| ESC |[ CONTROL | - C

208

Tables

Table 4-5 Bank Select Switches

(1 ) This switch write-enables RAM
and read-enables ROM.

(2) Two successive reads to this
switch enables RAM both for reading
and writing.

Switch

Write

Read

4KR/

\M Bank:

Address

RAM

ROM

First

Second

*C080

•

*C081

*C082

*C083

$C084

*C08S

SC086

SC087

$C088

$C089

$C08A

*C08B

$C08C

$C08D

$C08E

*C08F

•

Notes

Tables

209

Table 4-6 Auxiliary-memory Select
Switches

(1)When 80ST0REison, the PAGE2
switch selects main or auxiliary display
memory.

(2) When 80STQREison, the HIRES
switch enables you to use the PAGE2
switch to switch between the
high-resolution page-1 area in main
memory or auxiliary memory.

Name

Function

Location

Notes ^J

Hex

Decimal

RAMRD

Read auxiliary memory

$C003

49155

-16381

Write ^J

Read main memory

$C002

49154

-16382

Write |b^

Read RAMRD switch

*C013

49171

-16365

Read ^

RAMWRT

Write auxiliary memory

*C005

49157

-16379

Write

Write main memory

SC004

49156

-16380

Write

Read RAMWRT switch

*C014

49172

-16354

Read p^

80STORE

On: access display page

*C001

49153

-16383

Write

Off: use RAMRD, RAMWRT

$C000

49152

-16384

Write ET

Read 80STORE switch

$C018

49176

-16360

Read

PAGE2

Page 2 on (Aux. memory)

*C0SS

49237

-16299

Page 2 off (Main memory)

$C0S4

49236

-16300

Read PAGE 2 switch

$C01C

49180

-16356

Read

HIRES

On: access hi-res pages

*C057

49239

-16297

2 H

Off: use RAMRD, RAMWRT

$cose

49238

-16298

Read HI RES switch

$C01D

49181

-16355

Read ^J

ALTZP

Auxiliary stack & z. p.

$C009

49161

-16373

Write ~J

Main stack & zero page

$C008

49160

-16374

Write j^d

Read ALTZP switch

$coie

49174

-16352

Read

210

Tables

Table 4-10 Page 3 Vectors

Vector address
Decimal Hex

Vector function

1008 *3F0 Address of the subroutine that handles BRK requests

1009 *3F1 (normally $59, * FA).

1010
1011

*3F2
*3F3

Reset vector (see text).

1012 $3F4 Power-up byte (see text).

1 013

*3F5

1014

*3F6

1015

S3F7

Jump instruction to the subroutine that handles Applesoft
"&" commands (normally $4C, *58, *FF).

1016

*3F8

1017

*3F9

1018

$3FA

J ump instruct ion to the subroutine that handles user

( [CONTROL] - Y) commands.

1019

$3FB

1020

*3FC

1021

*3FD

Jump instruction to the subroutine that handles
non-maskable interrupts.

1022 »3FE Interrupt vector (address of the subroutine that handles

1023 *3FF interrupt requests).

Tables

211

Table 6-1 Peripheral-card I/O

Slot

Locations

Enabled by

Memory Locations

Note: The enabling signal is marked

$C090-*C09F

DEVICE SELECT'

with a prime, to indicate that it is an
active-low signal.

$C0A0-*C0AF

DEVICE SELECT'

$C0B0-*C0BF

DEVICE SELECT'

$C0C0-*C0CF

DEVICE SELECT'

*C0D0-*C0DF

DEVICE SELECT'

$C0E0-*C0EF

DEVICE SELECT'

$C0F0-*C0FF

DEVICE SELECT'

Table 6-2 Peripheral-card ROM

Slot

Locations

Enabled by

Memory Locations

Note: The enabling signal is marked

*C100-*C1FF

I/O SELECT'

with a prime, to indicate that it is an
active-low signal.

$C200-*C2FF

I/O SELECT'

$C300-*C3FF

I/O SELECT'

*C400-*C4FF

I/O SELECT'

$CS00-*C5FF

I/O SELECT'

$C600-*C6FF

I/O SELECT'

$C700-*C7FF

I/O SELECT'

212

Tables

— I IM.

Table 6-3 Peripheral-card RAM
Memory Locations

'Note: The RAM locations normally
allocated to slot 3 are taken over by
any card installed in the auxiliary slot.

Base
Address

Slot Number
3* 4 5

$0478 $0479 *047A *047B» *047C

$04F8 *04F9 $04FA *04FB* *04FC

$0578 $0579 $057A $0S7B* *057C

$05F8 *05F9 $05FA *05FB* $05FC

«0678 $0679 S067A *087B* $0G7C

*06F8 *06F9 $06FA $06FB» $0GFC

*0778 $0779 $077A $077B» *077C

*07F8 *07F9 *07FA *07FB* $07FC

$047D $047E *047F

$04FD *04FE *04FF

*057D $057E *057F

*05FD J05FE $05FF

*067D $067E $067F

*06FD $0GFE *06FF

*077D *077E $077F

$07FD *07FE $07FF

Tables

213

Table 6-4 Peripheral-card I/O Base
Addresses

Base
Address

Connector Number
3 4 5

*C080

$C090

$C0A0

*C0B0

*C0C0

*COD0

*C0E0

*C0FO

*C081

$C091

*C0A1

$C0B1

*C0C1

*C0D1

*C0E1

$C0F1

*C082

$C092

*C0A2

*C0B2

*C0C2

$C0D2

*C0E2

*C0F2

SC083

$C093

JC0A3

*C0B3

»C0C3

$C0D3

*C0E3

*C0F3

*C084

*C094

$C0A4

$C0B4

*C0C4

$C0D4

$C0E4

*C0F4

SC085

$C095

*C0A5

$C0B5

$C0C5

*C0D5

$C0E5

*C0F5

$C086

$C096

$C0A6

*C0B6

$C0C6

$C0D6

*C0E6

$C0F6

*C087

$C097

*C0A7

$C0B7

$C0C7

$C0D7

*C0E7

*C0F7

*C088

*C098

$C0A8

iC0B8

*C0C8

*C0D8

*C0E8

*C0F8

*C089

*C099

*C0A9

*C0B9

*C0C9

*C0D9

$C0E9

$C0F9

SC08A

*C09A

SCOAA

$C0BA

*C0CA

*C0DA

$C0EA

$C0FA

$C08B

$C09B

$C0AB

*C0BB

*C0CB

$C0DB

*C0EB

$C0FB

$C08C

SC09C

*C0AC

*C0BC

*C0CC

*C0DC

$C0EC

«C0FC

*C08D

*C09D

*C0AD

*C0BD

$C0CD

*C0DD

$C0ED

$C0FD

*C08E

*C09E

$C0AE

*C0BE

*C0CE

$C0DE

$C0EE

*C0FE

*C08F

*C09F

$C0AF

$C0BF

*C0CF

$C0DF

tCOEF

$C0FF

Table 6-5 I/O Memory Switches

Name

Function

Location
Hex Decimal

Notes

SL0TC3R0M Slot ROM at JC300 $C00B 49183 -1G373 Write

Internal ROM at $C300 *C00A 49162 -1G374 Write

Read SL0TC3R0M switch *C01 7 49175 -16361 Read

SLOTCXRDM Slot ROM at $CxOO *C007 49159 -16377 Write

Internal ROM at $CxOO *C006 49158 -16378 Write

Read SLQTCXROM switch $C015 49173 -16363 Read

214

Tables

■..-■■• ' '■:■■

■mm

' ' . '■-:■•'■:--

Appendix C

Directory of Built-in
Subroutines

Here is a list of useful subroutines in the Apple lie's Monitor. To
use these subroutines from machine-language programs, store
data into the specified memory locations or 6502 registers as
required by the subroutine and execute a JSR to the subroutine's
starting address. After the subroutine performs its function, it
returns with the 6502's registers changed as described.

Warning

For the sake of compatability between the Apple II Plus
and the Apple He, do not jump into the middle of Monitor
subroutines. The starting addresses are the same for all models of
the Apple II, but the actual code is different.

BELL Output a bell character

$FF3A

bell writes a bell ( [ control > g) character to the current output
device. It leaves the accumulator holding *87.

BELLI Send a beep to the speaker

$FBDD

belli generates a 1 kHz tone in the Apple lie's speaker for 0.1
second. It scrambles the A and X registers.

CLREOL Clear to end of line

*FC9C

clreol clears a text line from the cursor position to the right edge
of the window, clreol destroys the contents of A and Y.

CLEOLZ Clear to end of line

$FC9E

cleolz clears a text line to the right edge of the window, starting
at the location given by base address basl indexed by the
contents of the Y register. CLEOLZ destroys the contents of A
and Y.

Directory of Built-in Subroutines

217

CLREOP Clear to end of window $FC42

clreqp clears the text window from the cursor position to the
bottom of the window, clreop destroys the contents of A and Y.

CLRSCR Clear the low-resolution screen * F832 £■

CLRSCR clears the low-resolution graphics display to black. If you
call CLRSCR while the video display is in text mode, it fills the
screen with inverse-mode at-sign (@) characters. CLRSCR destroys
the contents of A and Y.

CLRTOP Clear the low-resolution screen * F836

clrtop is the same as CLRSCR (above), except that it clears only
the top 40 rows of the low-resolution display.

COUT Output a character $fded

CDUT calls the current character output subroutine. The character
to be output should be in the accumulator. COUT calls the
subroutine whose address is stored in csw (locations *36 and *37),
which is usually the standard character output CQUT1 .

COUT1 Output to screen $ fdf o

C0UT1 displays the character in the accumulator on the Apple lie's

screen at the current output cursor position and advances the

output cursor. It places the character using the setting of the

Normal/In verse location. It handles the control characters

I return I , linefeed, backspace, and bell. It returns with all registers

intact.

CROUT Generate a I RETURN ] *FD8E

crout sends a I return I character to the current output device.

CROUT1 1 RETURN [ with clear * FD8B

CRDUT1 clears the screen from the current cursor position to the
edge of the text window, then calls CROUT.

GETLN Get an input line with prompt $FD6A

GETLN is the standard input subroutine for entire lines of
characters, as described in Chapter 3. Your program calls getln

218 Directory of Built-in Subroutines

Jil

with the prompt character in location $33; getln returns with the
input line in the input buffer (beginning at location $200) and the
X register holding the length of the input line.

GETLNZ Get an input line

$FD67

GETLNZ is an alternate entry point for getln that sends a carriage
return to the standard output, then continues into GETLN.

GETLN1 Get an input line, no prompt

$FD6F

GETLN 1 is an alternate entry point for GETLN that does not issue a
prompt before it accepts the input line. If, however, the user
cancels the input line, either with too many backspaces or with a
[ CONTROL l -x, then GETLN1 will issue the contents of location
$33 as a prompt when it gets another line.

HLINE Draw a horizontal line of blocks

$F819

hline draws a horizontal line of blocks of the color set by setcol
on the low-resolution graphics display. Call hline with the vertical
coordinate of the line in the accumulator, the leftmost horizontal
coordinate in the Y register, and the rightmost horizontal
coordinate in location $2C. HLINE returns with A and Y scrambled,
X intact.

-Jli

-itf

-i«

HOME Home cursor and clear

$FC58

home clears the display and puts the cursor in the home position:
the upper left corner of the screen.

IOREST Restore all registers

$FF3F

iorest loads the 6502's internal registers with the contents of
memory locations $45 through $49.

IOSAVE Save all registers

$FF4A

iosave stores the contents of the 6502's internal registers in
locations $45 through $49 in the order A, X, Y, P, S. The contents
of A and X are changed and the decimal mode is cleared.

KEYIN Read the keyboard

$FD1B

keyin is the keyboard input subroutine. It reads the Apple lie's
keyboard, waits for a keypress, and randomizes the random

Directory of Built-in Subroutines

219

number seed at $4E-$4F. When a key is pressed, key IN removes
the blinking cursor from the display and returns with the keycode
in the accumulator. KEY IN is described in Chapter 3.

MOVE Move a block of memory $FE2C

move copies the contents of memory from one range of locations
to another. This subroutine is the same as the MOVE command in
the Monitor, except it takes its arguments from pairs of locations
in memory, low-byte first. The destination address must be in A4
($42-$43), the starting source address in A1 ($3C-$3D), and the
ending source address in A2 ($3E-$3F) when your program calls

MOVE.

NEXTCOL Increment color by 3 *F8SF

nextcol adds 3 to the current color (set by SETCOL) used for low-
resolution graphics.

PLOT Plot on the low-resolution screen $F800

plot puts a single block of the color value set by SETCOL on the
low-resolution display screen. The block's vertical position is
passed in the accumulator, its horizontal position in the Y
register, plot returns with the accumulator scrambled, but X and
Y intact.

PRBLNK Print 3 spaces *F948

prblnk outputs three blank spaces to the standard output device.
On return, the accumulator usually contains *ao, the X register
contains 0.

PRBL2 Print many blank spaces $ F94 A

PRBL2 outputs from 1 to 256 blanks to the standard output device.
Upon entry, the X register should contain the number of blanks
to be output. If X=$00, then PRBL2 will output 256 blanks.

PRBYTE Print a hexadecimal byte *fdda

prbyte outputs the contents of the accumulator in hexadecimal on
the current output device. The contents of the accumulator are
scrambled.

Directory of Built-in Subroutines

PREAD Read a hand control

*FB1E

pread returns a number that represents the position of a hand
control. You pass the number of the hand control in the X
register. If this number is not valid (not equal to 0, 1 , 2, or 3),
strange things may happen, pread returns with a number from
$00 to $FF in the Y register. The accumulator is scrambled.

PRERR Print ERR

$FF2D

prerr sends the word err, followed by a bell character, to the
standard output device. On return, the accumulator is scrambled.

PRHEX Print a hexadecimal digit

$FDE3

prhex prints the lower nybble of the accumulator as a single
hexadecimal digit. On return, the contents of the accumulator are
scrambled.

PRNTAX Print A and X in hexadecimal

$F941

prntax prints the contents of the A and X registers as a four-digit
hexadecimal value. The accumulator contains the first byte
output, the X register contains the second. On return, the
contents of the accumulator are scrambled.

RDCHAR Get an input character or esc code

$FD35

rdchar is an alternate input subroutine that gets characters from
the standard input subroutine, and also interprets the escape
codes listed in Chapter 3.

RDKEY Get an input character

$FD0C

RDKEY is the character input subroutine. It places a blinking cursor
on the display at the cursor position and jumps to the subroutine
whose address is stored in ksw (locations *38 and *39), usually
the standard input subroutine key IN, which returns with a
character in the accumulator.

READ Read a record from a cassette

$FEFD

READ reads a series of tones at the cassette input port, converts
them to data bytes, and stores the data in a specified range of

Directory of Built-in Subroutines

221

memory locations. Before calling READ, the address of the first
byte must be in A1 ($3C-$3D) and the address of the last byte in
A2 (*3E-3F.)

READ keeps a running Exclusive OR of the data bytes in CHKSUM
(*2E). When the last location has been filled, READ reads one more
byte and compares it with CHKSUM. If equal, READ sends out a beep,
and returns; if not, it sends "ERR" through cout, sends the beep,
and returns.

SCRN Read the low-resolution graphics screen *F871

SCRN returns the color value of a single block on the low-
resolution graphics display. Call it with the vertical position of the
block in the accumulator and the horizontal position in the Y
register. Call it as you would call PLOT (above). The color of the
block will be returned in the accumulator. No other registers are
changed.

SETCOL Set low-resolution graphics color $F864

setcol sets the color used for plotting in low-resolution graphics
to the value passed in the accumulator. The colors and their
values are listed in Table 2-7.

SETINV Set Inverse mode $FE 80

SETINV sets the dislay format to inverse. C0UT1 will then display all
output characters as black dots on a white background. The Y
register is set to *3F, all others are unchanged.

SETNORM Set Normal mode * FE84

SETNORM sets the display format to normal. C0UT1 will then display
all output characters as white dots on a black background. On
return, the Y register is set to *FF, all others are unchanged.

VERIFY Compare two blocks of memory $FE36

verify compares the contents of one range of memory to
another. This subroutine is the same as the verify command in
the Monitor, except it takes its arguments from pairs of locations
in memory, low-byte first. The destination address must be in A4
($42-$43), the starting source address in A1 ($3C-$3D), and the
ending source address in A2 ($3E-$3F) when your program calls

VERIFY.

Directory of Built-in Subroutines

VLINE Draw a vertical line of blocks

$F828

VL I NE draws a vertical line of blocks of the color set by SETCOL on
the low-resolution display. You should call VLINE with the
horizontal coordinate of the line in the Y register, the top vertical
coordinate in the accumulator, and the bottom vertical coordinate
in location *2D. VLINE will return with the accumulator scrambled.

WAIT Delay

$FCA8

WAIT delays for a specific amount of time, then returns to the
program that called it. The amount of delay is specified by the
contents of the accumulator. With A the contents of the
accumulator, the delay is 1/2(26+27A+5A"2) microseconds. WAIT
returns with the accumulator zeroed and the X and Y registers
undisturbed.

WRITE Write a record on a cassette

$FECD

■A

«j

WR ITE converts the data in a range of memory to a series of
tones at the cassette output port. Before calling WRITE, the
address of the first data byte must be in A1 (*3C-*3D) and the
address of the last byte in A2 ($3E-$3F). The subroutine writes
ten-second continuous tone as a header, then writes the data
followed by a one-byte checksum.

Directory of Built-in Subroutines

223

Appendix D

■3

Differences Between the
Apple He and the Apple II
Plus

The Apple He is the latest model Apple II, and it includes several
improvements over the older models. The improvements and
other differences are listed here in approximately the order you
are likely to encounter them: obvious differences first, technical
details later. Each entry in the list includes references to the
chapters in this manual where the item is described.

Full Keyboard

The Apple Me has a full 62-key uppercase and lowercase

key board. The ke yboard includes fully-operational |shift |
and [ CAPS LOc iTj keys. It also includes four directional arrow keys
for moving the cursor. Chapter 2 includes a description of the
keyboard. The cursor-motion keys are described in Chapter 3.

Apple Keys

The keyboard of the Apple He has two keys marked with the
Apple logo. These keys, called the | QPEN^-ftPPLE 1 and
| sol id-Apple I keys, are used with the ] RESET | key to select
special reset functions. They are connected to the buttons on the
hand controls, so they can be used for special functions in programs.

Lowercase Display

The Apple lie can display the full ASCII character set, uppercase
and lowercase. For compatibility with older Apple ll's, the
standard display character set includes flashing uppercase
instead of inverse-format lowercase; you can also switch to an
alternate character set with inverse lowercase and uppercase, but
no flashing. Chapter 2 includes a description of the display
character sets. Chapter 3 tells you how to switch display formats.

Full Keyboard

225

Optional 80-column Display

With the addition of an 80-column text card, the Apple Me can
display 80 columns of text. The 80-column display is completely
compatable with both graphics modes — you can even use it in
mixed mode. (If you prefer, you can use an old-style 80-column
card in an expansion slot instead.) Chapter 2 includes a
description of the 80-column display.

Additional Escape and Control Keys

The display features mentioned above (and many others not
mentioned) can be controlled from the keyboard by escape
sequences and from programs by control characters. Chapter 3
includes descriptions of those escape codes and control
characters.

Built-in Language Card

The 16K bytes of RAM you add to the Apple II Plus by installing
the Language Card is built into the Apple lie, giving it a standard
memory size of 64K bytes. In the Apple lie, this 16K-byte block
of memory is called the Bank-switched Memory. It is described in
Chapter 4.

Optional Auxiliary Memory

By installing an extended 80-column text card, you can add an
alternate 64K bytes of RAM to the Apple lie. Chapter 4 tells you
how to use the additional memory. (Compatibility note: the
extended 80-column text card also provides the 80-column
display option.)

Auxiliary Slot

In addition to the normal expansion slots there is a special slot
that is used either for the optional 80-column text card or for the
extended 80-column text card. This slot is identified in Chapter 1
and described in Chapter 7.

Back Panel and Connectors

The Apple lie has a metal back panel with space for several D-
type connectors. Each peripheral card you add comes with a
connector that you install in the back panel. Chapter 1 includes a
description of the back panel; for details, see the installation
instructions supplied with the peripheral cards.

226

Apple Me and Apple II Plus

Additional Soft Switches — Readable, Too

The additional display and memory features of the Apple lie are
controlled by soft switches like the ones on the Apple II Plus. On
the Apple lie, programs can also read the settings of the soft
switches. Chapter 2 describes the soft switches that control the
display features, and Chapter 4 describes the soft switches that
control the memory features.

Built-in Self Test

The Apple Me has additional built-in firmware that includes a self-
test routine. The self-test is intended primarily for testing during
manufacturing, but you can run it to be sure the Apple lie is
working correctly. The self-test is described in Chapter 4.

Forced Reset

Some programs on the Apple II Plus take control of the reset
function to keep users from stopping the machine and copying
the program. The Apple lie has a forced reset that writes over
the program in memory. By using the forced reset, you can
restart the Apple Me without turning power off and on and causing
unnecessary stress on the circuits. The forced reset is described
in Chapter 4.

....J

Interrupt Handling

Even though most application programs don't use interrupts, the
Apple Me provides for interrupt-driven programs. For example, the
80-column firmware periodically enables interrupts while it is
clearing the display (normally a long time to have interrupts
locked out). Interrupts are discussed in Chapter 6.

Vertical Sync for Animators

Programs with animation can now stay in step with the display
and avoid flickering objects in their displays. Chapter 7 includes a
description of the video generation and the vertical sync.

Apple He Signature Byte

A program can find out whether it's running on an Apple Me or on
an older model Apple II by reading the byte at location *FBB3 in
the System Monitor. In the Apple lie Monitor, this byte's value is
$06; in the Autostart Monitor (the standard Monitor on the
Apple II Plus), its value is $EA. (Note: if you start up with DOS

Additional Soft Switches — Readable, Too

227

and switch to Integer BASIC, the Autostart Monitor is active and
the value at location $FBB3 is $EA, even on an Apple Me.)
Obviously, there are lots of other locations that have different
values in the different versions of the Monitor; location $FBB3 was
chosen because it will have the value $06 even in future
revisions of the Apple lie Monitor.

Hardware Implementation

The hardware implementation of the Apple Me is radically different
from the Apple II and Apple II Plus. Three of the more important
differences are

• The custom ICs: the IOU and MMU;

• The video hardware, which uses ROM to generate both text
and graphics;

• The peripheral data bus, which is fully buffered.
All of these features are described in Chapter 7.

228

Apple Me and Apple II Plus

Glossary

6502: The microprocessor used in the Apple Me computer.

accumulator: The register in the 6502 microprocessor where
most computations are performed.

acronym: A word formed from the initial letters of a name or
phrase, such as laser, from Light Amplification by Stimulated
Emission of Radiation.

ADC: See analog-to-digital converter.

address: A number used to identify something, such as a
location in the computer's memory.

analog: Represented in terms of a physical quantity, such as a
voltage, frequency, length, or position, that can vary smoothly
and continuously over a range of values. For example, a
conventional 12-hour clock face (remember those?) is an analog
device that represents the time of day in terms of the angles of
the clock's hands. Compare digital.

analog-to-digital converter: A device that converts quantities
from analog to digital form. For example, the Apple He's hand
control converts the position of the control dial (an analog
quantity) into a discrete number (a digital quantity) that changes
abruptly even when the dial is turned smoothly.

AND: A logical operator that produces a true result if both of its
operands are true, a false result if either or both of its operands
are false; compare or, exclusive OR, NOT.

Apple He: A personal computer in the Apple II family,
manufactured and sold by Apple Computer.

Apple He 80-Column Text Card: A peripheral card made and
sold by Apple Computer that plugs into the Apple lie's auxiliary
slot and converts the computer's display of text from 40- to 80-
column width.

Glossary

231

Apple lie Extended 80-Column Text Card: A peripheral card
made and sold by Apple Computer that plugs into the Apple He's
auxiliary slot and converts the computer's display of text from 40-
to 80-column width while extending its memory capacity by 64K
bytes.

Applesoft: An extended version of the BASIC programming
language used with the Apple He computer. An interpreter for
creating and executing programs in Applesoft is built into the
Apple He system in firmware.

ASCII: American Standard Code for Information Interchange; a
code in which the numbers from to 1 27 stand for text
characters, used for representing text inside a computer and for
transmitting text between computers or between a computer and
a peripheral device.

assembler: A language translator that converts a program
written in assembly language into an equivalent program in
machine language.

assembly language: A low-level programming language in
which individual machine-language instructions are written in a
symbolic form more easily understood by a human programmer
than machine language itself.

auxiliary slot: The special expansion slot inside the Apple lie
used for the Apple 80-Column Text Card or Extended 80-Column
Text Card.

back panel: The rear face of the Apple lie computer, which
includes the power switch, the power connector, and connectors
for a video display device, a cassette tape recorder, and other
peripheral devices.

bandwidth: A measure of the range of frequencies a device can
handle. In the case of a video monitor, greater bandwidth
enables it to display more information; to display 80 columns of
text, a monitor should have a bandwidth of at least 12 MHz.

base address: In indexed addressing, the fixed component of an
address.

binary: The representation of numbers in terms of powers of
two, using the two digits and 1 . Commonly used in computers,
since the values o and 1 can easily be represented in physical
form in a variety of ways, such as the presence or absence of
current, positive or negative voltage, or a white or black dot on
the display screen.

232 Glossary

-3

binary operator: An operator that combines two operands to
produce a result; for example, OR is a binary logical operator.
Compare unary operator.

bit: A binary digit (0 or 1 ); the smallest possible unit of
information, consisting of a simple two-way choice, such as yes
or no, on or off, positive or negative, something or nothing.

bit bucket: The final resting place of all information; see write-
only memory.

board: See printed-circuit board.

boot: To start up a computer by loading a program into memory
from an external storage medium such as a disk. Often
accomplished by first loading a small program whose purpose is
to read the larger program into memory. The program is said to
"pull itself in by its own bootstraps"; hence the term
bootstrapping or booting .

bootstrap: See boot.

buffer: An area of the computer's memory reserved for a
specific purpose, such as to hold graphical information to be
displayed on the screen or text characters being read from some
peripheral device. Often used as an intermediary "holding area"
for transferring information between devices operating at different
speeds, such as the computer's processor and a printer or disk
drive. Information can be stored into the buffer by one device
and then read out by the other at a different speed.

bus: A group of wires that transmit related information, such as
the bits of an address, from one part of a computer system to
another.

byte: A unit of information consisting of a fixed number of bits;
on the Apple Me, one byte consists of eight bits and can hold any
value from o to 2SS.

card: See peripheral card.

carrier: A broadcast radio signal that is modulated in order to
transmit information.

carry flag: A status bit in the 6502 microprocessor, used in
addition and subtraction to hold the high-order bit (the carry bit).

cathode-ray tube: An electronic device, such as a television
picture tube, that produces images on a screen coated with
phosphors that emit light when struck by a focused beam of
electrons.

Glossary

233

central processing unit: See processor.

character: A letter, digit, punctuation mark, or other written
symbol used in printing or displaying information in a form
readable by humans.

character code: A number used to represent a text character for
processing by a computer system.

chip: The small piece of semiconducting material (usually silicon)
on which an integrated circuit is fabricated. The word chip
properly refers only to the piece of silicon itself, but is often used
for an integrated circuit and its package; see integrated circuit.

code: (1) A number or symbol used to represent some piece of
information in a compact or easily processed form. (2) The
statements or instructions making up a program.

cold start: The process of starting up the Apple Me when the
power is first turned on (or as if the power had just been turned
on) by loading the operating system into main memory, then
loading and running a program. Compare warm start.

command: A communication from the user to a computer
system (usually typed from the keyboard) directing it to perform
some immediate action.

compiler: A language translator that converts a program written
in a high-level programming language into an equivalent program
in some lower-level language (such as machine language) for
later execution. Compare interpreter.

component: A part; in particular, a part of a computer system.

composite video: A video signal that includes both display
information and the synchronization (and other) signals needed to
display it.

computer: An electronic device for performing predefined
(programmed) computations at high speed and with great
accuracy.

computer system: A computer and its associated hardware,
firmware, and software.

connector: a physical device such as a plug, socket, or jack,
used to connect one hardware component of a system to
another.

234 Glossary

control character: A character that controls or modifies the
way information is printed or displayed. Control characters have
ASCII codes between and 3i and are typed from the Apple Me
keyboard by holding down the rcDNTROL | k ey while typ ing some
other character. For example, the character | control | -m (ASCII
code 1 3) means "return to the beginning of the line" and is
equivalent to the I return | key.

controller card: A peripheral card that connects a device such
as a printer or disk drive to the Apple lie and controls the
operation of the device.

CPU: Central processing unit; see processor.

crash: To cease operating unexpectedly, possibly damaging or
destroying information in the process.

CRT: See cathode-ray tube.

cursor: A marker or symbol displayed on the screen that marks
where the user's next action will take effect or where the next
character typed from the keyboard will appear.

DAC: See digital-to-analog converter.

data: Information; especially information used or operated on by
a program.

debug: To locate and correct an error or the cause of a problem
or malfunction in a computer system. Typically used to refer to
software-related problems; compare troubleshoot.

decimal: The common form of number representation used in
everyday life, in which numbers are expressed in terms of
powers of ten, using the ten digits to 9.

default: A value, action, or setting that is automatically used by
a computer system when no other explicit information has been
given. For example, if a command to run a program from a disk
does not identify which disk drive to use, the Disk Operating
System will automatically use the same drive that was used in
the last operation.

defenestration: The act of throwing something through, from, or
out of a window. Not recommended handling of an Apple lie.

demodulate: To recover the information being transmitted by a
modulated signal; for example, a conventional radio receiver
demodulates an incoming broadcast signal to convert it into
sound emitted by a speaker.

Glossary

235

device: (1 ) A physical apparatus for performing a particular task
or achieving a particular purpose. (2) In particular, a hardware
component of a computer system.

device handler: See device driver.

device driver: A program that manages the transfer of
information between the computer and a peripheral device.

digit: (1) One of the characters o to 9, used to express numbers
in decimal form. (2) One of the characters used to express
numbers in some other form, such as o and 1 in binary or o to 9
and A to F in hexadecimal.

digital: Represented in a discrete (noncontinuous) form, such as
numerical digits. For example, contemporary digital clocks display
the time in numerical form (such as 2:57) instead of using the
positions of a pair of hands on a clock face. Compare analog.

digital-to-analog converter: A device that converts quantities
from digital to analog form.

DIP: See dual in-line package.

disassembler: A language translator that converts a machine-
language program into an equivalent program in assembly
language, more easily understood by a human programmer. The
opposite of an assembler.

disk: An information storage medium consisting of a flat, circular
magnetic surface on which information can be recorded in the
form of small magnetized spots, similarly to the way sounds are
recorded on tape.

disk controller card: A peripheral card that connects one or two
disk drives to the Apple lie and controls their operation.

disk drive: A peripheral device that writes and reads information
on the surface of a magnetic disk.

diskette: A term sometimes used for the small (5-1/4-inch)
flexible disks used with the Apple Disk II drive.

Disk II drive: A model of disk drive made and sold by Apple
Computer for use with the Apple Me computer; uses 5-1/4-inch
flexible ("floppy") disks.

Disk Operating System: An optional software system for the
Apple Me that enables the computer to control and communicate
with one or more Disk II drives.

display: (1) Information exhibited visually, especially on the
screen of a display device. (2) To exhibit information visually. (3)
A display device.

236 Glossary

display device: A device that exhibits information visually, such
as a television receiver or video monitor.

display screen: The glass or plastic panel on the front of a
display device, on which images are displayed.

DOS: See Disk Operating System.

dual in-line package: An integrated circuit packaged in a narrow
rectangular box with a row of metal pins along each side; similar
in appearance to an armored centipede.

edit: To change or modify; for example, to insert, remove,
replace, or move text in a document.

editor: A program that enables the user to create and edit
information of a particular form; for example, a fexr editor or a
graphics editor.

effective address: In machine-language programming, the
address of the memory location on which a particular instruction
actually operates, which may be arrived at by indexed addressing
or some other addressing method.

error message: A message displayed or printed to notify the
user of an error or problem in the execution of a program.

escape mod e: A s tate of the Apple lie computer, entered by
pressing the |esc | key, in which certain keys on the keyboard
take on special meanings for positioning the cursor and
controlling the display of text on the screen.

escap e sequence: A sequence of keystrokes beginning with the
I ESC | key, used for positioning the cursor and controlling the
display of text on the screen.

exclusive OR: A logical operator that produces a true result if
one of its operands is true and the other false, a false result if its
operands are both true or both false; compare OR, and, NOT.

execute: To perform or carry out a specified action or sequence
of actions, such as those described by a program.

expansion slot: A connector inside the Apple Me computer in
which a peripheral card can be installed; sometimes called
peripheral slot.

firmware: Those components of a computer system consisting of
programs stored permanently in read-only memory. Such
programs (for example, the Applesoft interpreter and the Apple
lie Monitor program) are built into the computer at the factory;
they can be executed at any time but cannot be modified or
erased from main memory. Compare hardware, software.

Glossary

237

fixed-point: A method of representing numbers inside the
computer in which the decimal point (more correctly, the binary
point) is considered to occur at a fixed position within the
number. Typically, the point is considered to lie at the right end
of the number, so that the number is interpreted as an integer.
Compare floating-point.

flexible disk: A disk made of flexible plastic; often called a
"floppy" disk. Compare rigid disk.

floating-point: A method of representing numbers inside the
computer in which the decimal point (more correctly, the binary
point) is permitted to "float" to different positions within the
number. Some of the bits within the number itself are used to
keep track of the point's position. Compare fixed-point.

GAME I/O connector: A special 16-pin connector inside the
Apple lie, originally designed for connecting hand controls to the
computer, but also used for connecting some other peripheral
devices. Compare hand control connector.

graphics: (1) Information presented in the form of pictures or
images. (2) The display of pictures or images on a computer's
display screen. Compare text.

hand control: An optional peripheral device that can be
connected to the Apple lie's hand control connector and has a
rotating dial and a pushbutton; typically used to control game-
playing programs, but can be used in more serious applications
as well.

hand control connector: A 9-pin connector on the Apple lie's
back panel, used for connecting hand controls to the computer.
Compare GAME I/O connector.

hardware: Those components of a computer system consisting
of physical (electronic or mechanical) devices. Compare
software, firmware.

hertz: The unit of frequency of vibration or oscillation, also called
cycles per second; named for the physicist Heinrich Hertz and
abbreviated Hz. The current provided by a standard power outlet
alternates at a rate of 60 hertz; that is , it changes polarity 60
times each second. The Apple lie's 6502 microprocessor
operates at a clock frequency of 1 million hertz, or 1 megahertz
(MHz).

238 Glossary

J
3
3
3

1
J

•3

.' j

hexadecimal: The representation of numbers in terms of
powers of sixteen, using the sixteen digits to 9 and A to F.
Hexadecimal numbers are easier for humans to read and
understand than binary numbers, but can be converted easily
and directly to binary form: each hexadecimal digit corresponds
to a sequence of four binary digits, or bits.

high-level language: A programming language that is relatively
easy for humans to understand. A single statement in a high-
level language typically corresponds to several instructions of
machine language.

high-order byte: The more significant half of a memory address
or other two-byte quantity. In the Apple lie's 6502
microprocessor, the low-order byte of an address is usually
stored first and the high-order byte second.

high-resolution graphics: The display of graphics on

the Apple lie's display screen as a six-color array of points, 280

columns wide and 192 rows high.

hold time: In computer circuits, the amount of time a signal
must remain valid after some related signal has been turned off;
compare setup time.

Hz: See hertz.

IC: See integrated circuit.

information: Facts, concepts, or instructions represented in an
organized form.

index: (1) A number used to identify a member of a list or table
by its sequential position. (2) A list or table whose entries are
identified by sequential position. (3) In machine-language
programming, the variable component of an indexed address,
contained in an index register and added to the base address to
form the effective address.

indexed addressing: A method of specifying memory addresses
used in machine-language programming.

index register: A register in a computer processor that holds an
index for use in indexed addressing. The Apple He's 6502
microprocessor has two index registers, called the x register and
the Y register.

input: (1) Information transferred into a computer from some
external source, such as the keyboard, a disk drive, or a modem.
(2) The act or process of transferring such information.

Glossary

239

instruction: A unit of a machine-language or assembly-language
program corresponding to a single action for the computer's
processor to perform.

integer: A whole number, with no fractional part; represented
inside the computer in fixed-point form. Compare real number.

integrated circuit: An electronic component consisting of many
circuit elements fabricated on a single piece of semiconducting
material, such as silicon; see chip.

interface: The devices, rules, or conventions by which one
component of a system communicates with another.

interface card: A peripheral card that implements a particular
interface (such as a parallel or serial interface) by which the
computer can communicate with a peripheral device such as a
printer or modem.

interpreter: A language translator that reads a program written
in a particular programming language and immediately carries out
the actions that the program describes. Compare compiler.

interrupt: A temporary suspension in the execution of a program
by a computer in order to perform some other task, typically in
response to a signal from a peripheral device or other source
external to the computer.

inverse video: The display of text on the computer's display
screen in the form of black dots on a white (or other single
phosphor color) background, instead of the usual white dots on a
black background.

I/O: Input/output; the transfer of information into and out of a
computer. See input, output.

I/O device: Input/output device; a device that transfers
information into or out of a computer. See input, output,
peripheral device.

I/O link: A fixed location that contains the address of an input/
output subroutine in the Apple Me Monitor program.

K: Two to the tenth power, or 1024 (from the Greek root kilo,
meaning one thousand); for example, 64K equals 64 times 1024,
or 65,536.

keyboard: The set of keys built into the Apple lie computer,
similar to a typewriter keyboard, for typing information to the
computer.

keystroke: T he act of pre ssing a single key or a combination of
keys (such as [ CONTROL ] -C) on the Apple Me keyboard.

240 Glossary

kilobyte: A unit of information consisting of 1K (1024) bytes, or
8K (8192) bits; see K.

KSW: The symbolic name of the location in the Apple He's
memory where the standard input link is stored; stands for
"keyboard switch." See I/O link.

language: See programming language.

language translator: A system program that reads a program
written in a particular programming language and either executes
it directly or converts it into some other language (such as
machine language) for later execution. See interpreter,
compiler, assembler.

load: To transfer information from a peripheral storage medium
(such as a disk) into main memory for use; for example, to
transfer a program into memory for execution.

location: See memory location.

logical operator: An operator, such as and, that combines
logical values to produce a logical result.

low-level language: A programming language that is relatively
close to the form that the computer's processor can execute
directly. Low-level languages available for the Apple He include
6502 machine language and 6502 assembly language.

low-order byte: The less significant half of a memory address or
other two-byte quantity. In the Apple lie's 6502 microprocessor,
the low-order byte of an address is usually stored first and the
high-order byte second.

low-power Shottkey: A type of TTL integrated circuit having
lower power and higher speed than a conventional TTL
integrated circuit.

low-resolution graphics: The display of graphics on the
Apple lie's display screen as a sixteen-color array of blocks,
40 columns wide and 48 rows high.

LS: See low-power Shottkey.

machine language: The form in which instructions to a
computer are stored in memory for direct execution by the
computer's processor. Each model of computer processor (such
as the 6502 microprocessor used in the Apple lie) has its own
form of machine language.

Glossary

241

main memory: The memory component of a computer system
that is built into the computer itself and whose contents are
directly accessible to the processor.

memory: A hardware component of a computer system that can
store information for later retrieval; see main memory, random-
access memory, read-only memory, read-write memory,
write-only memory.

memory location: A unit of main memory that is identified by
an address and can hold a single item of information of a fixed
size; in the Apple lie, a memory location holds one byte, or eight
bits, of information.

memory-resident: (1 ) Stored permanently in main memory, as
firmware. (2) Held continually in main memory even while not in
use, as the Disk Operating System.

MHz: Megahertz; one million hertz. See hertz.

microcomputer: A computer, such as the Apple lie, whose
processor is a microprocessor.

microprocessor: A computer processor contained in a single
integrated circuit, such as the 6502 microprocessor used in the
Apple lie.

microsecond: One millionth of a second; abbreviated ;u,s.

millisecond: One thousandth of a second; abbreviated ms.

mode: A state of a computer or system that determines its
behavior.

modem: Modulator/demodulator; a peripheral device that
enables the computer to transmit and receive information over a
telephone line.

modulate: To modify or alter a signal so as to transmit
information; for example, conventional broadcast radio transmits
sound by modulating the amplitude (amplitude modulation, or
AM) or the frequency (frequency modulation, or FM) of a carrier
signal.

monitor: See video monitor.

Monitor program: A system program built into the Apple lie in
firmware, used for directly inspecting or changing the contents of
main memory and for operating the computer at the machine-
language level.

nanosecond: One billionth (in British usage, one thousand-
millionth) of a second; abbreviated ns.

242 Glossary

network: A collection of interconnected, individually controlled
computers, together with the hardware and software used to
connect them.

nibble: A unit of information equal to half a byte, four bits, or
fifty cents; can hold any value from to 1 5. Sometimes spelled
nybble.

NOT: A unary logical operator that produces a true result if its
operand is false, a false result if its operand is true; compare and,

OR, exclusive DR.

NTSC: (1) National Television Standards Committee; the
committee that defined the standard format used for transmitting
broadcast video signals in the United States. (2) The standard
video format defined by the NTSC.

object code: See object program.

object program: The translated form of a program produced by
a language translator such as a compiler or assembler; also
called object code. Compare source program.

op code: See operation code.

operand: A value to which an operator is applied.

operating system: A software system that organizes the
computer's resources and capabilities and makes them available
to the user or to application programs running on the computer.

operation code: The part of a machine-language instruction that
specifies the operation to be performed; often called op code.

operator: A symbol or sequence of characters, such as + or and,
specifying an operation to be performed on one or more values
(the operands) to produce a result.

OR: A logical operator that produces a true result if either or both
of its operands are true, a false result if both of its operands are
false; compare exclusive or, and, not.

output: (1 ) Information transferred from a computer to some
external destination, such as the display screen, a disk drive, a
printer, or a modem. (2) The act or process of transferring such
information.

page: (1 ) A screenful of information on a video display,
consisting on the Apple lie of 24 lines of 40 or 80 characters
each. (2) An area of main memory containing text or graphical
information being displayed on the screen. (3) A segment of main
memory 256 bytes long and beginning at an address that is an
even multiple of 256 bytes.

Glossary

243

page zero: See zero page.

parallel interface: An interface in which many bits of information
(typically eight bits, or one byte) are transmitted simultaneously
over different wires or channels. Compare serial interface.

PC board: See printed-circuit board.

peripheral: At or outside the boundaries of the computer itself,
either physically (as a peripheral device) or in a logical sense
(as a peripheral card).

peripheral bus: The bus used for transmitting information
between the Apple lie computer and peripheral devices
connected to the computer's expansion slots.

peripheral card: A removable printed-circuit board that plugs
into one of the Apple lie's expansion slots and expands or
modifies the computer's capabilities by connnecting a peripheral
device or performing some subsidiary or peripheral function.

peripheral device: A device, such as a video monitor, disk
drive, printer, or modem, used in conjunction with a computer.
Often (but not necessarily) physically separate from the computer
and connected to it by wires, cables, or some other form of
interface, typically by means of a peripheral card.

peripheral slot: See expansion slot.

phase: (1) A stage in a periodic process; a point in a cycle; for
example, the 6502 microprocessor uses a clock cycle consisting
of two phases called 4>0 and </>1. (2) The relationship between
two periodic signals or processes; for example, in NTSC color
video, the color of a point on the screen is expressed by the
instantaneous phase of the video signal relative to the color
reference signal.

pipelining: A feature of a processor that enables it to begin
fetching the next instruction before it has finished executing the
current instruction. All other things equal, processors that have
this feature run faster than those without it.

pointer: An item of information consisting of the memory
address of some other item.

pop: To remove the top entry from a stack.

port: The point of connection, usually a physical connector,
between a computer and a peripheral device, another computer,
or a network.

244 Glossary

power supply: The hardware component of a computer that
draws electrical power from a power outlet and converts it to the
forms needed by other hardware components.

printed-circuit board: A hardware component of a computer or
other electronic device, consisting of a flat, rectangular piece of
rigid material, commonly fiberglass, to which integrated circuits
and other electronic components are connected.

printer: A peripheral device that writes information on paper in a
form easily readable by humans or literate monkeys.

processor: The hardware component of a computer that
performs the actual computation by directly executing instructions
represented in machine language and stored in main memory.

program: (1) A set of instructions describing actions for a
computer to perform in order to accomplish some task,
conforming to the rules and conventions of a particular
programming language. (2) To write a program.

programming language: A set of rules or conventions for
writing programs.

prompt: To remind or signal the user that some action is
expected, typically by displaying a distinctive symbol, a reminder
message, or a menu of choices on the display screen.

prompt character: A text character displayed on the screen to
prompt the user for some action. Often also identifies the
program or component of the system that is doing the prompting;
for example, the prompt character ] is used by the Applesoft
BASIC interpreter, > by Integer BASIC, and * by the system
Monitor program. Also called prompting character.

prompt message: A message displayed on the screen to
prompt the user for some action. Also called prompting
message.

push: To add an entry to the top of a stack.

radio-frequency modulator: A device for converting the video
signals produced by a computer to a form that can be accepted
by a television receiver.

RAM: See random-access memory.

random-access memory: Memory in which the contents of
individual locations can be referred to in an arbitrary or random
order. This term is often used incorrectly to refer to read-write
memory, but strictly speaking both read-only and read-write

Glossary

memory can be accessed in random order. This misuse of the
term random-access is an attempt to confuse new users,
creating a rite of passage and an excellent market for glossaries
of computer terms. Compare read-only memory, read-write
memory, write-only memory.

raster: The pattern of parallel lines making up the image on a
video display screen. The image is produced by controlling the
brightness of successive dots on the individual lines of the raster.

read: To transfer information into the computer's memory from a
source external to the computer (such as a disk drive or modem)
or into the computer's processor from a source external to the
processor (such as the keyboard or main memory).

read-only memory: Memory whose contents can be read but
not written; used for storing firmware. Information is written into
read-only memory once, during manufacture; it then remains
there permanently, even when the computer's power is turned
off, and can never be erased or changed. Compare read-write
memory, random-access memory, write-only memory.

read-write memory: Memory whose contents can both be read
and written; often misleadingly called random-access memory, or
RAM. The information contained in read-write memory is erased
when the computer's power is turned off, and is permanently lost
unless it has been saved on a more permanent storage medium,
such as a disk. Compare read-only memory, random-access
memory, write-only memory.

real number: A number that may include a fractional part;
represented inside the computer in floating-point form. Compare
integer.

register: A location in a computer processor where an item of
information, such as a byte, is held and modified under program
control. Registers in the 6502 microprocessor include the
accumulator (A), two index registers (x and Y), the stack pointer
(S), the processor status register (P), and the program counter
(PC). The PC register holds two bytes (sixteen bits); the other
registers hold one byte (eight bits) each.

return address: The point in a program to which control returns
on completion of a subroutine.

RF modulator: See radio-frequency modulator.

rigid disk: A disk made of a hard, nonflexible material. Compare
flexible disk.

246 Glossary

-4

3
3
3
3

ROM: See read-only memory.

routine: A part of a program that accomplishes some task
subordinate to the overall task of the program.

run: (1) To execute a program. (2) To load a program into main
memory from a peripheral storage medium, such as a disk, and
execute it.

save: To transfer information from main memory to a peripheral
storage medium for later use.

screen: See display screen.

scroll: To change the contents of all or part of the display
screen by shifting information out at one end (most often the top)
to make room for new information appearing at the other end
(most often the bottom), producing an effect like that of moving a
scroll of paper past a fixed viewing window. See viewport,
window.

serial interface: An interface in which information is transmitted
sequentially, one bit at a time, over a single wire or channel.
Compare parallel interface.

setup time: The amount of time a signal must be valid in
advance of some event; compare hold time.

silicon: A non-metallic, semiconducting chemical element from
which integrated circuits are made. Not to be confused with silica
— that is, silicon dioxide, such as quartz, opal, or sand — or
with silicone, any of a group of organic compounds containing
silicon.

soft switch: A means of changing some feature of the Apple lie
from within a program; specifically, a location in memory that
produces some special effect whenever its contents are read or
written.

software: Those components of a computer system consisting of
programs that determine or control the behavior of the computer.
Compare hardware, firmware.

source code: See source program.

source program: The original form of a program given to a
language translator such as a compiler or assembler for
conversion into another form; sometimes called source code.
Compare object program.

space character: A text character whose printed representation

is a blank space, typed from the keyboard by pressing the |SPftCE l
bar.

Glossary

247

stack: A list in which entries are added or removed at one end
only (the top of the stack), causing them to be removed in LIFO
(last-in-first-out) order.

string: An item of information consisting of a sequence of text
characters.

strobe: (1) An event, such as a change in a signal, that triggers
some action. (2) A signal whose change is used to trigger some
action.

subroutine: A part of a program that can be executed on
request from any point in the program, and which returns control
to the point of the request on completion.

system: A coordinated collection of interrelated and interacting
parts organized to perform some function or achieve some
purpose.

television receiver: A display device capable of receiving
broadcast video signals (such as commercial television) by
means of an antenna. Can be used in combination with a radio-
frequency modulator as a display device for the Apple Me
computer. Compare video monitor.

television set: See television receiver.

terminal: A device consisting of a typewriterlike keyboard and a
display device, used for communicating between a computer
system and a human user. Personal computers such as the
Apple Me typically have all or part of a terminal built into them.

text: (1) Information presented in the form of characters readable
by humans. (2) The display of characters on the Apple lie's
display screen. Compare graphics.

text window: An area on the Apple lie's display screen within
which text is displayed and scrolled.

transistor-transistor logic: (1) A family of integrated circuits
used in computers and related devices. (2) A standard for
interconnecting such circuits that defines the voltages used to
represent logical zeros and ones.

troubleshoot: To locate and correct the cause of a problem or
malfunction in a computer system. Typically used to refer to
hardware-related problems; compare debug.

TTL: See transistor-transistor logic.

unary operator: An operator that applies to a single operand;
for example, the minus sign (-) in a negative number such as -6
is a unary arithmetic operator. Compare binary operator.

248 Glossary

-J

user: The person operating or controlling a computer system.

user interface: The rules and conventions by which a computer
system communicates with the person operating it.

vector: (1) The starting address of a program segment, when
used as a common point for transferring control from other
programs. (2) A memory location used to hold a vector, or the
address of such a location.

video: (1) A medium for transmitting information in the form of
images to be displayed on the screen of a cathode-ray tube. (2)
Information organized or transmitted in video form. (3) An early
space pioneer.

video monitor: A display device capable of receiving video
signals by direct connection only, and which cannot receive
broadcast signals such as commercial television. Can be
connected directly to the Apple He computer as a display device.
Compare television receiver.

viewport: All or part of the display screen, used by an
application program to display a portion of the information (such
as a document, picture, or worksheet) that the program is
working on. Compare window.

warm start: The process of restarting the Apple lie after the
power is already on, without reloading the operating system into
main memory and often without losing the program or information
already in main memory. Compare cold start.

window: (1 ) The portion of a collection of information (such as a
document, picture, or worksheet) that is visible in a viewport on
the display screen; compare viewport. (2) A viewport. (3) A flat,
rectangular panel, usually made of silica, used in many archaic
structures as a human-to-nature interface.

word: A group of bits of a fixed size that is treated as a unit; the
number of bits in a word is a characteristic of each particular
computer.

wraparound: The automatic continuation of text from the end of
one line to the beginning of the next, as on the display screen or
a printer.

write: To transfer information from the computer to a destination
external to the computer (such as a disk drive, printer, or
modem) or from the computer's processor to a destination
external to the processor (such as main memory).

Glossary

249

write-only memory: A form of computer memory into which
information can be stored but never, ever retrieved, developed
under government contract in 1975 by Professor Homberg T.
Farnsfarfle. Farnsfarfle's original prototype, approximately one
inch on each side, has so far been used to store more than 100
trillion words of surplus federal information. Farnsfarfle's critics
have denounced his project as a six-million-dollar boondoggle,
but his defenders point out that this excess information would
have cost more than 250 billion dollars to store in conventional
media. Compare read-only memory, read-write memory,
random-access memory.

x register: One of the index registers in the 6502
microprocessor.

Y register: One of the index registers in the 6502
microprocessor.

zero page: The first page (256 bytes) of the Apple lie's memory,
also called page zero. Since the high-order byte of any address
in this page is zero, only the low-order byte is needed to specify
a zero-page address; this makes zero-page locations more
efficient to address, in both time and space, than locations in any
other page of memory.

250

Glossary

-4

3
3
3

3
5
3

-4

bibliography

Bibliography

Apple Computer, Inc.: Apple lie Applesoft Reference Manual;
Apple Computer Inc., 1982, Cupertino, CA. Apple product number
A2L2004

— Apple He Applesoft Tutorial Manual; Apple Computer Inc.,
1982, Cupertino, CA. Apple product number A2L2003

— Apple II BASIC Programming Manual; Apple Computer Inc.,
1978, Cupertino, CA. Apple product number A2L0005

— Apple II Monitors Peeled; Apple Computer Inc., 1978,
Cupertino, California. Apple product number D2L0013

— Apple He Owner's Manual; Apple Computer Inc., 1982,
Cupertino, CA. Apple product number A2L2001

— Programmer's Aid #1 Installation and Operating Manual;
Apple Computer Inc., 1978, Cupertino, California. Apple product
number A2L001 1

Leventhal, Lance: 6502 Assembly Language Programming;
Osborne/McGraw-Hill, 1979, Berkeley, CA.

Synertek, Incorporated: Hardware Manual; Synertek Incorporated,
1976, Santa Clara, CA. Apple product number A2L0002

— Programming Manual; Synertek Incorporated, 1976, Santa
Clara, CA. Apple product number A2L0003

Watson, Allen, III: "More Colors for Your Apple"; Byte, Vol. 4,
No. 6, June, 1979. Byte Publications, Inc, Peterborough, NH

— "Simplified Theory of Video Graphics, Part I"; Byte, Vol. 5,
No. 11, November, 1980. Byte Publications, Inc, Peterborough,
NH

Bibliography

— "Simplified Theory of Video Graphics, Part II"; Byte, Vol. 5,
No. 12, December, 1980. Byte Publications, Inc. Peterborough,
NH

Wozniak, Steve: "System Description: The Apple II"; Byte, Vol. 2,
No. 5, May, 1977. Byte Publications, Inc. Peterborough, NH

— "SWEET16: The 6502 Dream Machine"; Byte, Vol. 2,

No. 10, October, 1977. Byte Publications, Inc, Peterborough, NH

tt — I

254

Bibliography

- I

■J
5

Index

idex

A1 77-8

A1H 77

A1L 77

A 2 77-8

A2H 77

A2L 77

A4 77-8

A4H 77

A4L 77

absolute address 108

accumulator 54, 78-9, 126-8,

140, 185, 187
ADC 188
addition 1 03
address bus 6, 35, 140, 142,

169-70
address decoding, I/O 1 64
address space 63,140,148
addresses

absolute 1 08

base 64, 126-129

in Monitor commands 88

Mini-assembler 113

multiplexed 151

RAM 151

relative 108, 114, 126
addressing, relative 108, 114,

126
addressing, zero-page 113
altcharset soft switch 20, 28,

45, 145
alternate character set 19-21, 45,

52-4, 158
ALTZP soft switch 74-7, 143
analog input memory locations 40

••<..., •,■ ; ••■.■;
analog inputs 37, 39, 167
and function 52

annunciator memory locations 40

annunciators 35, 37, 79, 164,

167
Any-key-down 15, 164
Any-key-down flag 13,15
Apple II

character sets 20

compatibility 76

GETLN 58

making lie resemble 44

memory use 68
Apple II BASIC Programming

Manual 1 3
Apple II Plus

character sets 20

compatibility 76

cursor-motion keys 56

GETLN 58

making lie resemble 44

memory use 68

reset 70
Apple keys 12, 17, 38, 40
Apple Mini-assembler 57, 110-14
Applesoft BASIC

and bank-switched memory 68

and page zero 64, 66, 92

and reset routine 80

and I/O subroutines 43

decimal addresses with 13,27

interpreter 6, 148

prompt 57

returning to 102

statements 45
Applesoft Reference Manual 6
Applesoft Tutorial 6, 58
arrow keys 12, 58
ASCII codes 12-1 7, '21
ASCII character set 5, 16, 19
ASL 188

assemblers 108, 110
Assembler/Editor 110

Index

257

258

assembly language
and auxmove 77
and bank switching 70
and display pages 29
and I/O links 130
and indirect addressing 64
and machine language 108-9
and standard subroutines 43
hexadecimal addresses with 13
prompt character 57
with Mini-assembler 110-113

asterisk 57, 87

audio cassettes 36, 98

automatic repeat 1 1

Autostart Monitor 47

auxiliary memory 26, 30, 71-78

auxiliary RAM 63, 71, 79

auxiliary slot 7, 21, 71
and reset routine 79
and slot 3 46, 123-4, 132-3
signals 174-5

auxiliary-memory subroutines 76

auxiliary-RAM enable signals 175

AUXMOVE subroutine 76-8

back panel 8

backspace 58

backspace character 58

bandwidth 17

bank switches 69

bank switching 68-71

bank-switched memory 68-72,

73-4

and reset 79
bank-switched RAM 68-70, 74,

80, 110
base addresses 64,126-129
BASIC

and auxiliary memory 71

and getln 56-7

and I/O 103, 129-30

and reserved memory 71

and soft switches 29

and stop-list mode 50

and taping data 37

and zero page 64

compared to machine
language 107

invoking Monitor from 87

reading analog inputs 40

reading switch input 38

returning to from Mini-
assembler 112

returning to from Monitor 88,

102

Index

BASIC, Applesoft

see Applesoft BASIC
BASIC, Integer

see Integer BASIC
bcc 188
BCS 188
BEQ 188

bell subroutine 36
BIT 188

bit patterns, high-resolution 161
bit, high-order

see high-order bit
bit-mapped 24
black-and-white monitor 24
blanking intervals 153
blanking, horizontal 153
blanking, vertical 154
blinking cursor 43, 54, 87, 110
BM I 1 88
BNE 188
bootstrap 80
borrow 1 85
bpl 188

BRK 97, 108, 140, 188
BRK requests 82
BRK vector 131
buffer, bus 170
buffer, input 56-8, 64, 106
buffers, display 24, 65
buffers, three-state 170
built-in 80-column firmware

see 80-column firmware
built-in subroutines 76-78
bus buffer 170
bus, address 6, 35, 140, 142,

169, 170
bus, data 170
BVC 188
BVS 189

CALL -151 87, 110, 112
cancel line 58
CAPS LOCK key 12,13,17,44,

58
card, language 68, 70, 121
cards, peripheral see peripheral

cards and 80-column text card
carry bit 77, 78, 187
CAS 151
cassette I/O 11, 35-6, 40, 98,

164, 166
cassette recorder 8, 36, 166
central processing unit 6, 140,

143, 151

-4

CH 50-1

character generator 158-62
Character output Switch

130
character set, alternate

45, 52-4, 158
character set, ASCII 5
character set, primary

53, 79, 158
character sets 19
characters, lowercase
characters, uppercase
checksum 99, 100
circuit board, main 6,

139, 169, 174
circuit, protection 139
circuits, I/O 164-168
circumflex 111, 114
CLC 189
CLD 189

clear-strobe switch 13
CLEOLZ 46
CLI 189
clock 141
clock rate 140
clock signals 141, 142
CLREDL 46
CLRE0P 46
CLRGAT' 146, 177
CLV 189
CMP 189

codes, hex operation 1 94
codes, intruction 188-192
cold-start reset 80
colon (in Monitor commands)

115
color monitor 24, 25, 160
color signal 160-2
color television set 24,
color television, NTSC
color-burst gate 1 53
colors 22

high-resolution 24-5

low-resolution 23, 160
Column-address Strobe 151
command characters 88
complementary decimal 13
composite video 17, 163
connectors (see also slots)

D-type miniature 37, 167

for cassette recorder 8

for hand-controls 8, 37, 167

for video monitor 8
constant, time 39
continue basic command 102
control characters 50

CDNTRDL key 12, 13, 17, 50, 164
CONTROL - OPEN-APPLE - RESET

i 48,129,

CONTROL

-B

102, 116

19-21,

CONTROL

-c

50, 88, 102, 116

CONTROL

-D

130

, 16, 19

CONTROL

-E

116

19-21, 45,

CONTROL

-K

103, 130

CONTROL

- OPEN-APPLE - RESET

20, 44, 53

CONTROL

-P

46 ,102, 117

20, 44, 53

CONTROL

- RESET 79-81, 88

CONTROL

-s

37, 121,

CONTROL

- SOLID-APPLE -

RESET

CONTROL

-u

93,

160
25

161

CONTROL -Y 106

controller card, disk drive 80
counter, horizontal 153, 155
counter, program 109, 111
counter, vertical 153, 155
counters, video 153, 157
COUT 43, 46, 47, 58, 101
C0UT1 47-53, 57, 129,

130
cover 4

CPU 6, 140, 143, 151
CPX 189
CPY 189
CSW 48, 129, 130
CSWH 129
CSNL 129
currents, supply 138
cursor

blinking 43, 54, 87, 110

checkerboard 43, 110

motion 56

plus sign 56

position 49-51, 57, 79
cursor-control keys 12, 55, 56
CV 50, 51
cycle stealing 149

D-type miniature connector 37,

167
daisy chain, priority 170
data bus 170
data str6be 37, 167'
debounce 164
DEC 189
decimal 13, 27
decimal, complementary 13
decoder, keyboard character 6,

13, 149, 164

Index

259

DEVICE SELECT' 122, 169, 174

DEX 189

DEY 189

Diagnostics ROM 148

direct-memory access signal 170

disassembler 108

disk drive controller card 80

Disk Operating System see DOS

display, video 11, 17-34, 152-62

80-column 46, 159, 175

buffers 65

display memory 154

display mode 27

display pages 26-30, 65,
72, 74

formats 19-20, 52-3

flashing format 19-20, 44, 52-3

high-resolution 161

inverse 19-20, 46, 52-3, 101

low-resolution 160

mixed-mode 19, 27

normal 19-20, 52-3, 101

soft switches 28
DMA IN 170
DMA OUT 170
DMA' 144, 169-170
DOS

and reset 80

and Monitor 87, 102

I/O links 47,130

link address storage 65

page zero usage 64, 67, 92

RAM addressing 129
DOS Manual 65, 80, 81, 130
DOS Tool Kit 110

DOWN-ARROW 12

dynamic RAM 143, 145, 149, 151

editing 58
EIA 163

Electronic Industries
Association 163
EN80' 144, 175, 177
environmental specifications 137
E0R 190
ERR 100
error message 83
errors 1 1 1

ESC key 12, 13, 54, 56

ESC CONTROL -Q 46
escape codes 55
escape mode 56
examine command 98
exclusive-0R 81, 82
expansion ROM 123-125

expansion slot 3 45, 46, 79
expansion slots 7, 80, 121-33,

169-174
extended 80-column text card 71

F866G 111, 117
FF69G 112, 117
firmware (see also 80-column

firmware)

built-in I/O 43-58

on peripheral cards 121
flashing display format 19-20, 44,

52-3
flip-flop 124

forced cold-start reset 79, 81
format, inverse 19-20, 46,

52-57, 101
FP 47
functions

AND 52

stop-list 50

G (Monitor command) 117

Game I/O 167

GAME I/O socket 168

game inputs 37, 167

gate, color-burst 153

GETLN 43, 53, 56-8, 64, 88

GO command 97,102,107,111

gotoXY 49

GR 147, 174, 178

graphics 22-34

high-resolution 18-19,23-5,29,
161

low-resolution 18-19, 22-3, 160

mixed-mode 27
grounded outlet 138

hand controls 8, 37, 167
hand-control connector 37
hand-control input 35, 167
Hardware Manual 141
hex operation codes 1 94
hexadecimal 13, 14, 23, 27, 61,

88, 113
hexadecimal arithmetic 103
high-level languages 29, 43,

107 (see also names of

languages)
high-order bit

and cassette I/O 37

and color determination
24-5, 162

260

Index

and display format 53

and state of soft switches 29, 36

of switch input byte 38
high-resolution bit patterns 161
high-resolution graphics 18-19,

23-5, 29, 161
high-resolution graphics

colors 25, 161
high-resolution Page 1 24, 30,

65, 74
high-resolution Page 2 24, 30, 65
HIRES soft switch 28, 74-5, 143,

145
HOME 46

horizontal blanking 153
horizontal counter 153,155
horizontal sync 1 53

I (Monitor command) 116
I/O

address decoding 164

built-in devices 11-41

built-in firmware 43-58

circuits 168

drivers 121

links, standard 46, 79,
129-130

memory locations 122, 132

subroutines 43-47, 87
I/D SELECT' 123, 124, 169, 172
I/O STROBE' 124, 125, 172
I/OREST 126
I/DSAVE 126
IC G

IN* 103, 130
iN#n command 130
INC 190
index register 61, 106, 127, 140,

187
index register Y 78, 187
index register X 78, 128, 187
indirect addressing 64
INH' 144, 169, 173
input buffer 56-58, 64, 106
input devices 11-41
input features 53-58
INPUT statement 56-7
input, hand-control 35, 167
Input-Output Unit see IOU
inputs

analog 37, 39

game 167

switch 38, 167
instructions, assembly

language 108-1 1

instructions, 6502 186
INT 47, 110
INT IN 131, 170
INT OUT 131, 170
INTBASIC 110

INTC3R0M soft switch 46
Integer BASIC

and bank-switched memory 68

and the Mini-assembler 110

and the old Monitor 47

and rdkey 54

and reset routine 70, 80

and standard I/O
subroutines 43

complementary decimal
with 13, 27

page zero usage 64, 67

prompt character 57

returning to 102

statements 45
integrated circuit 6
interface 13

interpreter, Applesoft BASIC 6
interpreter, Integer BASIC 110
interrupt handler 131
interrupt priority 131
interrupt requests 131,170
interrupt vectors 81-2,131
interrupt-handling routine 131
interrupts 46, 82, 126, 131, 170
intruction codes 188-192
intruction cycle 140
inverse command 101
inverse display format 19-20, 44,

46, 52-3, 101
INX 190
I NY 190
IOU 6, 7, 143, 145, 153, 155,

164-7
IRQ vector 131, 140
IRQ' 131, 170, 173

joystick 37

JMP intruction 79, 106, 190
JSR instruction 127, 190
Jump to Subroutine 127

keyboard 5, 11-17, 43-4, 88, 164
KEYBOARD command 103
keyboard data 13,28
keyboard encoder 6, 13, 149,

164
Keyboard input Switch 130

Index

261

keyboard strobe 13, 15, 28, 79,

164
keyboard-input buffer 64
KEY IN 43, 47, 53-56, 129-30
keypad 165
KSW 54, 130
KSWH 130
KSWL 130

L (Monitor command) 117
language card 68, 70, 121
languages (see also names of

languages)

assembly 29, 108-9, 113

high-level 29, 43, 107

machine 107-110
last opened location 89-91, 94,

96, 107, 109
LDA 190
LDX 190

LDY 190

LED 4, 166

LEFT-ARROW key 12, 55
light-emitting diode 4, 166
line voltage 137
link addresses 47, 65, 130
link registers 130
link, input 54
link, output 48
links, standard I/O 47, 79, 129-

30
list command 108-10,113
loudspeaker 5, 166
low-order bits 13,24
low-order byte 78
low-resolution graphics 18-19, 22-

3, 160
low-resolution graphics blocks 22
low-resolution graphics colors 23,

160
lowercase characters 20, 44, 53
LSR 191

M (Monitor command) 115
machine language 107-10
main circuit board 6, 37, 121,

139, 169, 174
main memory 30, 73, 75, 77,

78, 121
memory

auxiliary 26, 30, 71-78

bank-switched 68-71 , 74, 79

display 29-34, 154
I/O 122,131

main 30, 73,75, 77, 78, 127

progammable see RAM

read-only see ROM
memory addressing 148-151
memory dump 89-91
memory locations

I/O devices 11, 13, 27, 28, 41

peripheral card 122
Memory Management Unit 6,

143, 151
memory maps 29, 31-4, 62, 63
memory organization 61-83
memory page 1 61 , 73
memory page 2 61
memory page 3 65
memory page zero see zero

page
memory pages 61
memory range 91
microprocessor, 6502 6, 140-142

accumulator 126

circuitry 170

contents of registers 97

data bus 170

interrupt requests 131

instructions 107, 186

memory addressing 61, 64,
121, 124, 148-151

stack 64, 73

timing 142, 149, 151
Mini-assembler 57, 110-14
Mini-assembler commands 1 1 7
mixed soft switch 28, 145
mixed-mode display 19,27
MMU 6, 143, 151
mnemonic 108, 111, 113, 114
Monitor, Autostart 47
Monitor, old 47, 110
Monitor, System 43, 57, 63-6, 87-

117, 129-31, 148
Monitor commands 88-107,109,

115-7
Monitor ROM 148
monitor, black-and-white 22, 24
monitor, color 24, 25, 160
monitor, video 8, 17, 152
move command 94-7, 105
multiplexed addressing 150-1

N (Monitor command) 116

n C0NTR0L-P 129

National Television Standards
Committee see NTSC

next changeable location 89,
93, 94, 96

91,

262

Index

NMI 140

NMI' 170, 173

NOP 191

normal command 101

normal display format 19-20, 52-

3, 101
NTSC 17, 18, 24, 152, 160, 163
NTSC color television 25
numeric pad 165
nybble 22, 160

old Monitor 47, 110
opcode 110, 194
open-apple key 12,17,38,41,

81
operand 110, 111
operating temperature 137
operation codes 110,194
dra 191

outlet, grounded 138
output devices 11,17-41

annunciator 37

cassette 36

strobe 38

video display 17-34
output link 48
output routine, standard 57
overflow 78
overflow bit 78

paddles 167

page 1, memory 61, 73

page 3, memory 65

Page 1, high-resolution 24, 30,

65, 71
Page 1, text 26, 32, 65, 74
Page 2, high-resolution 24, 30,

65
Page 2, text 26, 27
page zero see zero page
PAGE2 soft switch 28, 30, 72-5,

143, 145, 161
pages, memory 61
PAL 143, 147, 151
Pascal 43, 107
PEEK 14, 27, 38, 39
period (.) 89
peripheral cards 8, 121-133, 138,

169-74

base addresses 127-9

I/O space 122

ROM space 122, 133

subroutines 126

peripheral devices 121-33, 169-

74
peripheral hardware 137
peripheral slots see expansion

slots
PG2 158, 161
PHA 191
phi 141, 142, 144, 146, 147,

151, 167, 174, 177
phi 1 141, 142, 147, 151, 173,

178
phi 2 141
phone jacks 8
PHP 191
pipelining 6, 140
PLA 191
PLP 191

plus sign (inverse format) 56
pointer, stack 64, 79, 140, 185,

187
POKE 27

potentiometers 39
power 4, 5
power connector 139
power consumption 138
power cord 6, 138
power supply 5,138-9,
power switch 6
power-on reset 79
power-up byte 81-2
PR* 103, 130
PR'O 46
PR#3 46
PR'n 129
PREAD 40
primary character set 19-21, 45,

53, 79, 158
PRINT statement 45, 130
printer command 102, 103
priority daisy chain 170
processor status register 1 87
program counter 109,111
program, assembly language 43
programmable memory see RAM
programmable storage 61,63
Programmed Array Logic

device 143, 147, 151
PROM 121-3
prompt characters 43, 56, 57

* 87

> 110

! 111
protection circuit 139
pseudo-random number 54
pull-up resistors 167
pushbutton switches 167

Index

263

Q3 141, 144, 146, 147, 151, 173

R (Monitor command) 99-100,

116
R/W 144, 146, 176
R/W80 175
RAM

and Monitor 47

and peripheral cards 121

and reset 79

auxiliary 63, 71, 79

bank-switched 68-70, 74, 80,
110

dynamic 143, 145, 149, 151

memory access, 61,149

reserved memory 63

second bank 70
RAMRD 73-75, 143
RAMWRT 73-75, 143
random number 54
random number, pseudo 54
random-access memory see

RAM
RAS 151

RDKEY 43, 47, 54, 56
reading data 28
reading to secondary I/O 35
READ command 99-100, 116
read only memory see ROM
read/write signal 142
recorder, cassette 8, 36, 166
registers 97, 126, 140, 187 (see

also accumulator)

index 61, 127, 140, 185, 187

link 130

processor status 140,187

program counter 187

size of 140

stack pointer 64, 79, 140, 185,
187
relative addressing 108,114,126
repeating keys 1 1
RES' 173

reserved memory pages 63
RESET key 12, 13, 17, 79-81,

83
reset routine 1 7, 79-83
reset vector 70, 79-83
RESET' 146
reset, cold-start 80
reset, forced cold-start 81
reset, power-on 79
reset, warm-start 80

resident program 81
resistor, variable 168
resistors, pull-up 167
restricted-case mode 58
Return from Subroutine 108, 127,

129, 130, 192
retype 58

RF modulator 17, 152
RIGHT-ARROW key 12, 58
R0L 191
rollover 1 1
ROM 6
and bank-switched memory

68-70, 73, 79
and memory addressing 61,

148
and the Monitor 47
character-generator 161
Diagnostics 148
expansion 123-5
Monitor 148

peripheral card 125, 132-3
RDR 191
routines 217-223
routines, interrupt-handling 131
Row-address Strobe 151
RTI 192
RTS 108, 127, 129, 130, 192

SBC 192
scrolling 49, 50
SEC 192

second bank of RAM
SED 192
SEI 192

self test 17, 83, 131,
SHIFT key 12, 13,
short circuits 5, 139
signal, read/write 142
signals, clock 141-2
signals, timing 141-2, 149, 159,

161, 162, 169
slot number 126-30
slot, auxiliary see auxiliary slot
slot, expansion see expansion

slots
SL0TC3R0M 132, 133, 143
SL0TCXR0M 132, 143
slots, ventilation 137
soft switches 27, 92, 127, 143,

145 (see also names of

switches)

and self test 83

annunciator 37

auxiliary memory 75

bank select 69, 73-6, 79

148
17, 164

a
a

a
i

264

Index

-a

-41

definition 15

display 11, 28

game I/O 167

keyboard 1 64

speaker 35
SOLID-APPLE key 12, 17, 38,

41, 81, 83
sounds 5
speaker 5, 11, 35, 164, 166

memory locations 41

soft switches 35
special function keys 17
specifications, environmental 137
STA 192

stack 64, 74, 78, 126
stack overflow 64
stack pointer 64, 79, 140, 185,

187
standard I/O links 47, 79, 129-31
standard I/O subroutines 43-57,

87
standard input routine see key in
standard output routine see COUT
startup 80
stop-list feature 50
stop-list function 50
strobe

column-address 151

data 37, 167

keyboard 13,15,28,79,164

row-address 151
strobe bit 14

strobe output 35, 38, 40, 167
STX 192
STY 192

subcarrier, color 25, 160
subroutines 217-223

auxiliary memory 76-79

built-in 76-79

I/O 43-58, 87

peripheral-card 126

standard input 54, 56
subtraction 103
supply currents 138
supply voltage 138
switch 38
switch 1 38
switch inputs 38, 167
switches, pushbutton 167
symbolic labels 110
SYNC 146, 153, 174
sync, horizontal 153
Synertek Hardware Manual 141
Synertek Programming

Manual 1 1 3

see Monitor,

36, 98, 166

17,
137

22, 24, 25, 152

165
145

System Monitor
System

tape recorder

TAX 192

TAY 192

television set

temperature

ten-key numeric pad

text soft switch 28,

text 19-21,26-32

text card see 80-column text card

text card, extended 80-column 71

text characters see character

sets
text Page 1 26, 32, 65, 74
text Page 2 26, 27
text window 48-52, 79
text, 40-column see 40-column

text
text, 80-column see 80-column

text
three-state buffers 170
time constant 39
timing signals 141-2, 149, 159,

161, 162, 169
toggle 35

transistor-transistor logic 167
TSX 192
TTL 167

TV set see television set
TXA 193
txs 193

TYA 193

UP-ARRDW 12

uppercase characters 20, 44, 53
uppercase-restrict mode 45
user

v (Monitor command) 115
validity-check byte 80, 82
variable resistor 168
VBL 28, 145, 154
vectors 47, 65, 71

interrupt 81-2, 131

reset 70, 79-83
ventilation slots 137
VERIFY command 96, 97,
vertical blanking 145, 154
vertical counter 153, 155
video counters 153,157

105

video display see display, video
video modulator 17, 18

Index

265

video monitor 8, 17, 152
video output signal 25,163
voltage, line 137, 138
voltage, supply 138

w (Monitor command) 98-100,

116
warm-start reset 80
window, text 48-52
WNDW 146, 153, 176
write command 98-100, 116
write-protect 69
writing data 28
writing to secondary I/O 35

X register 78, 187
XFER 76-9

Y register 78, 128, 187

zero page 61,64,66-7,73-8,92,

113, 126
zero-page addressing 113

Numbers

14M 141, 147, 177

3.58 MHz color signal 1 60-2

3.58M (PAL signal) 147

3.58M (slot 7 signal) 174

3.58M (auxiliary slot signal) 176

3D0G 102

40-column text 18, 26, 44, 154

6502 microprocessor

see microprocessor, 6502
6502 stack 73
6502B microprocessor 6,140
7M 141, 147, 173, 178
80-column display 7, 30, 46, 72,

159, 175
80-column firmware 45-47,110,

123-24

CDUT1 subroutine 52

deactivating 102

in ROM 148

KEY IN subroutine 54, 56

memory use 131, 133

reset routine 79
80-column text 18, 21, 30, 44,

154, 162, 175
80-column text card 7, 17, 21,

46, 71, 133
80-column text mode 26

80COL soft switch 28, 145, 161
80 STORE soft switch 28, 30, 72-

75, 143, 175
80VID soft switch 158, 161
80VID' signal 146, 147, 177

Cast of Characters

A
?

114

111
57

> 57, 110
] 57
* 57, 87
! 57, 1 1 1
. 89

$ (in addresses) 113
$ (with Monitor command) 111,

117
: (in Monitor commands) 93, 115
+ (inverse format) 56

CDNTR0L -B 102, 116

CONTROL -C 50, 88, 102, 116

CONTROL -D 130

CONTROL -E 116

CONTROL -K 103, 130

CONTROL -P 46, 102, 117

CONTROL -S 50

CONTROL -U 46

CONTROL -Y 106
4>0 141, 142, 144, 146, 147, 150,

167, 174, 177
<f>1 141, 142, 147,
cf>2 141

150, 173, 178

266

Index

■b&Jtfi

^cippkz computer

20525 Mariani Avenue

Cupertino, CA 95014

(408) 996-1010

TLX 171576 030-0357B

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